Can a Revocably-Divorced Woman Go Out during `Iddah?
Question

Is it permissible for a woman who is observing `Iddah following divorce in a minor sense to stay overnight outside her family’s house, if her work requires that of her, to attend a conference, for example, in another region of the same country, not because she herself wants to stay overnight outside the house?
Praise be to Allah.Difference between revocable and irrevocable divorces
If she has been divorced three times , then she is irrevocably-divorced and it is not permissible for her to go back to her (first) husband unless she marries someone else, then this marriage ends as a result of divorce or death of the (second) husband.
However, if her husband issued a first or second divorce, then left her until her `Iddah ended and did not take her back, then she is divorced in a minor sense (revocable divorce).
An example of that is if the husband divorced her in return for some compensation – which is known as Khul` . In this case, she becomes divorced from him as soon as the legal procedure of Khul` is completed, even if her `Iddah has not yet ended.
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said in Ash-Sharh Al-Mumti` (12/468):
“Separation , meaning being fully divorced in a complete sense, is of two types:

Separation in a major sense (irrevocable), which is after three divorces.
Separation in a complete but minor sense (revocable), which is divorce in return for compensation (Khul`).

If a man had divorced his wife twice previously, then he divorced her a third time, we say that this is divorce in a complete and major sense, meaning that it is not permissible for her to go back to her (first) husband unless she marries someone else, then this (second) marriage ends as a result of divorce or death of the husband.
If he divorced her in return for compensation (Khul`), then this becomes a complete divorce in a minor sense, which means that it is permissible for him to take her back, and so on.”
He (may Allah have mercy on him) also said, in Ash-Sharh Al-Mumti` (12/130):
“The woman who is fully divorced in a minor sense is the one whose husband separates from her by means of Khul`. It is called minor because it is permissible for the husband who has divorced her by Khul` to remarry her during the `Iddah and afterwards. As for divorce in a complete and major sense, this refers to one who has been divorced three times. Based on that, divorced women during the `Iddah period are of three types:

One who may be taken back; she is the woman in `Iddah whose husband has the right to take her back without a new marriage contract.
One who is divorced in a minor sense; she is the woman whose husband may remarry her with a new marriage contract, but has no right to take her back (without a new marriage contract). However, he may make a new marriage contract with her. Any woman in `Iddah who cannot be taken back except with a new marriage contract, her divorce is complete in a minor sense.
One who is divorced in a major sense. This is the woman who was divorced with the last of three divorces. It is not permissible for her to go back to her (first) husband unless she marries someone else, then this marriage ends as a result of divorce or death of the (second) husband, subject to the well-known conditions.”

Can a revocably-divorced woman go out during `Iddah?
If the `Iddah of a woman who has been divorced revocably ends, then the one who divorced her no longer has any right of guardianship over her, and she may go out or stay overnight wherever she wishes.
If her `Iddah has not yet ended, then the revocably-divorced woman who is observing `Iddah is permitted to go out of her house, and she is not forbidden to do that, unlike the one whose husband has died, but she should not go out of her house unless her husband gives her permission , because she is still under his guardianship; she has the same rights to maintenance, accommodation, staying overnight in his house, and so on, that other wives have, and she has the same duties as other wives.
Similarly, `Abdullah ibn `Umar (may Allah be pleased with him) used to say: If a man has divorced his wife once or twice, she should not go out of his house except with his permission.” (Narrated by Ibn Abu Shaybah in his Musannaf, 4/142)
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said: The most correct view is that if a woman is divorced revocably, then she is like a wife who has not been divorced; in other words, she may go out to visit her neighbours or relatives, or to go to the mosque and attend a lesson, and the like. She is not like a woman whose husband has died.
With regard to the verse in which Allah, may He be Exalted, says (interpretation of the meaning): “Do not turn them out of their [husbands'] houses, nor should they [themselves] leave [during that period]” [At-Talaq 65:1], what is meant by turning them out is separation. In other words, she should not leave the home and go out and live elsewhere.” (Fatawa Nur `Ala Ad-Darb)
Can a divorced woman attend conferences?
With regard to attending a conference in another region of the same country, if what is meant is that the woman will be travelling from her place of residence, it is not permissible for her to do that unless she is accompanied by a Mahram (her husband or a relative whom she is permanently prohibited from marrying).
Al-Bukhari (3006) and Muslim (1341) narrated from Ibn `Abbas (may Allah be pleased with him) that he heard the Prophet (blessings and peace of Allah be upon him) say: “No man should be alone with a [non-Mahram] woman, and no woman should travel except with a Mahram.”
A man stood up and said: O Messenger of Allah, I have enlisted in such and such a campaign, and my wife has gone out for Hajj. He said: “Go and do Hajj with your wife.”
And Allah knows best.