Mourning Period in Islam for a Wife
Question

What are the regulations concerning the ‘iddah of a widow?
I have been told that she cannot leave her husband's house at all during the 4 months and 10 days, but others say she must only be careful to leave only for true needs and must never sleep away from her husband's house during this time.
I have also been told that she cannot wash or comb her hair. The latter especially seems contrary to Islam regarding cleanliness. 
A detailed response would be greatly appreciated. Jazakum Allahu khayran
Praise be to Allah.How long should a woman mourn her husband?
Allah says (interpretation of the meaning):
And those of you who die and leave wives behind them, they (the wives) shall wait (as regards their marriage) for four months and ten days, then when they have fulfilled their term, there is no sin on you if they (the wives) dispose of themselves in a just and honourable manner (i.e., they can marry). And Allah is Well-Acquainted with what you do. [Al-Baqarah 2:234]
And those of you who die and leave behind wives should bequeath for their wives a year’s maintenance and residence without turning them out, but if they (wives) leave, there is no sin on you for that which they do of themselves, provided it is honourable (e.g., lawful marriage). And Allah is All-Mighty, All-Wise. [Al-Baqarah 2:240]
Umm `Atiyyah reported that the Messenger of Allah (peace and blessings of Allah be upon him) said: No woman should mourn for a dead person for more than three days , except for a husband, (in which case the period of mourning is) four months and ten days . She should not wear any coloured clothes, only simple dress. She should not apply kohl to her eyes, or use perfume, except for a little qust or izfar (types of perfume), when she cleans herself after finishing her period. (Muslim, 2739)
Umm Habibah bint Abi Sufyan reported that when the news of her father’s death reached her, she called for some perfume and wiped it on her forearms, and said: I do not need it, but I heard the Prophet (peace and blessings of Allah be upon him) say: It is not permitted for a woman who believes in Allah and the Last Day to mourn for any dead person for more than three days, except for a husband, (in which case the period of mourning is) four months and ten days. (Al-Bukhari, 4926)
Umm Salamah, the wife of the Prophet (peace and blessings of Allah be upon him) reported that the Prophet (peace and blessings of Allah be upon him) said: The woman whose husband has (recently) died should not wear clothes dyed with safflower or mishq (a reddish clay), or dye her hair, or use kohl. (Al-Nasai, 3479, and others)
Zaynab bint Ka’b ibn ‘Ujrah reported that al-Furayyah bint Malik ibn Sinan, the sister of Abu Sa’id al-Khudri, told her that she came to the Messenger of Allah (peace and blessings of Allah be upon him) and asked him whether she should go back to her people among Banu Khudrah. Her husband had gone out in pursuit of some rebellious slaves of his, and when he caught up with them at the edge of al-Qadum, they killed him. She said: I asked the Messenger of Allah (peace and blessings of Allah be upon him) whether I should go back to my family, because my husband had not left me a place to live that belonged to him, or any money for provisions. The Messenger of Allah (peace and blessings of Allah be upon him) said yes, so I started to leave, and I had reached the hujrah (room) or the mosque, when the Messenger of Allah (peace and blessings of Allah be upon him) called me or told someone to call me. So I came back, and he asked me, What did you say? I repeated the story I had told him about my husband. He said: Stay in your house for the specified length of time. So I spent my `iddah there, four months and ten days. At the time of ‘Uthman, he sent word to me asking about this, so I told him, and he followed what I said and judged in accordance with it. Muhammad ibn Bashshar told us that Yahya ibn Sa’id informed us that Sa’d ibn Ishaq ibn Ka'b ibn ‘Ujrah informed us of something similar. Reported by al-Tirmidhi, who said: This is a sahih hasan hadith. The majority of scholars among the Companions of the Prophet (peace and blessings of Allah be upon him) and others followed this hadith and did not allow a widow to move out of her husband’s home until her `iddah was over. (Sunan al-Tirmidhi, 1125)
How should a widow observe her `iddah?
On the basis of the texts quoted above, the scholars have defined the rules governing widows and described how the widow's mourning should affect her life. These rules may be summed up as follows:

It is forbidden for the recently-widowed woman to use perfume, whether on her body or on her clothes
It is forbidden for the recently-widowed woman to adorn herself with things like henna or facial make-up, or to use kohl unnecessarily, or to use anything else that may make her beautiful and attractive to others.
It is forbidden for the recently-widowed woman to wear attractive clothes, such as clothes dyed with safflower or saffron, or other types of red dyes and colours that are used for adornment.
It is forbidden for the recently-widowed woman to wear jewellery.
It is forbidden for the recently-widowed woman to spend the night outside her own home , meaning the home of her deceased husband, except for some Islamically legitimate reason, such as her being afraid for her own safety, or being evicted by the landlord of rented premises, etc. If a recently-widowed woman needs to go out for medical treatment, to attend legal proceedings in court, to take exams in school , or to go shopping when she has no-one who can do this for her, then she should do these things during the day, so long as she comes back home to her husband’s house before Maghrib (sunset).
She is forbidden to marry or draw up a marriage contract; even engagement is forbidden, unless it is merely hinted at and not stated clearly.

From the above, it is clear that Islam gives the husband immense rights. The wife should give up wearing adornments and perfume, and should stay in her husband’s home during this period because of those rights. These rules also pay attention to her psychological state at this time when she has lost her support. 
Even though these rules are so clear, many people have still fallen prey to many different kinds of bid`ah when it comes to mourning, so they forbid a woman to do things that are not forbidden in Islam, and they fabricate lies and introduce bid`ah into the Religion of Allah. 
Shaykh ‘Abd al-’Aziz ibn Baz said:
“Some people may think and imagine that a recently widowed woman should not speak to anyone, or speak to anyone on the telephone, or have a bath more than once a week, or walk barefoot in her house, or go outside in the moonlight, or other such nonsense which has no basis. But in fact she is allowed to walk barefoot or with shoes in her house, to do whatever she needs to in her house, to cook food for herself and her guests, to walk in the moonlight on the roof or in the garden of her house, to take a bath whenever she wants, to speak to whomever she wants so long as it is decent talk, to shake hands with other women and with her mahram relatives (close relatives such as father, brother, etc.) but not with non-mahrams, and to remove her head covering so long as there are no non-mahrams present. She should not use henna, saffron or perfume, and she is not allowed to get engaged. A hint is permissible but not a clear statement. And Allah is the source of strength.” (Fatawa Islamiyah, 3/316)
Ruling on wearing black in mourning for the dead
Shaykh ‘Abd-Allah ibn Jibrin said: 
“Wearing black to mourn the deceased is a form of bid`ah , and the wives of the deceased only need to avoid fancy clothes, adornment, jewellery, makeup and perfume during the mourning period. Neglecting regular work during the mourning period is also a form of bid`ah. The recently widowed woman should still take care of cooking, cleaning, washing dishes, laundry, etc., and there is no sin involved in doing so. And Allah knows best. (Al-Lulu al-Makin, 39)
Shaykh Muhammad ibn Salih al-Uthaymin said:
“Wearing special clothes to accept condolences is a form of bid`ah, in our opinion, because it could indicate that one is discontent with the decree of Allah, may He be glorified. (Fatawaa al-Ta’ziyah, 38)
He also said:
“Wearing black as a sign of mourning is a false symbol that has no basis. At times of bereavement a person should do what is taught by Islam, which is to say: Inaa Lillahi wa innaa ilayhi raji’un. Allahumma’jurni fi musibati wakhluf li khayran minha (To Allah we belong and unto Him is our return. O Allah, recompense me for my affliction and replace it for me with something better). As regards wearing some special clothing, such as wearing black and so on, this has no basis, and it is false and reprehensible conduct.” (Fatawa Islamiyah, 3/313)
And Allah knows best.