Can Muslim Women Wear Pants?
Question

Is it permissible to wear wide pants with a garment that covers the entire body and comes a hand span above the ankles, with no slits in the garment, and the garment is not see-through or tight?
Praise be to Allah.Islamic dress code for females
The clothing in which a woman appears before non-Mahram men must meet eight conditions: 

It should cover the entire body , including the face and hands. 
It must be wide and loose , not showing the size of her limbs or the shape of her body.
It should not be thin, showing the colour of her skin.
It should not be an adornment in and of itself, such as clothing decorated with embroidery.
It should not be perfumed.
It should not resemble the clothing of men.
It should not resemble the dress of disbelieving women.
It should not be a dress of fame and vanity. (See Adab Az-Zifaf by Shaykh Al-Albani (may Allah have mercy on him), p. 177; Hijab Al-Mar’ah Al-Muslimah, p. 16-111; ‘Awdat Al-Hijab, 3/145-163) 

Can Muslim women wear pants?
Based on this, a woman should not appear in front of men wearing pants or trousers because:

They show the shape of the woman’s legs
Wearing them is an imitation of men 

Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) said:
“I think that the Muslims should not follow these fashions and kinds of clothes that come to us from here and there. Many of them are not in accordance with proper Islamic dress which involves covering the woman completely, like the short or very tight or thin clothes. That includes pants, because they show the size of a woman’s legs, as well as her stomach, waist, breasts, etc. Wearing it comes under the description given in the authentic Hadith: “there are two types of the people of Hell whom I have not seen: people with whips like the tails of cattle, with which they strike the people, and women who are clothed yet naked, walking with an enticing gait, with something on their heads that looks like the humps of camels, leaning to one side. They will never enter Paradise or even smell its fragrance, although its fragrance can be detected from such and such a distance.”  This Hadith was narrated by Muslim, 2128.” (Majmu` Faaawa Ash-Shaykh Ibn `Uthaymin) 
Can Muslim women wear pants under a Jilbab?
With regard to wearing pants under a Jilbab, there is nothing wrong with that, rather it is more covering and more protective, if the Jilbab is wide and concealing and does not have any splits that show what is underneath it. 
Shaykh `Abd Ar-Razzaq `Afifi (may Allah have mercy on him) said: 
“If a woman wears pants and puts over them a wide garment then she will not be resembling men, so long as she wears them underneath her garments.” (Fatawa Ash-Shaykh`Abd Ar-Razzaq `Afifi, p. 573) 
The basic principle is that the woman’s Jilbab should be wide and cover the tops of her feet, because of the report narrated by At-Tirmidhi (1731), An-Nasa’i (5336), Abu Dawud (4117) and Ibn Majah (3580) from Ibn ‘Umar (may Allah be pleased with him) who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “Whoever lets his garment drag out of pride, Allah will not look at him on the Day of Resurrection.” Umm Salamah said: “What should women do with their hems?” He said: “Let them down by a handspan.” She said: “But then their feet will be uncovered.” He said: “Then a cubit, but no more than that.” This Hadith was classed as authentic by Al-Albani in Sahih Sunan At-Tirmidhi. 
Al-Baji (may Allah have mercy on him) said: 
“The words of Umm Salamah (may Allah be pleased with her) regarding lengthening the hem by a hand span – “But then their feet will be uncovered” – show that this length was not sufficient to cover them, because the movement of her feet when walking quickly, combined with the shortness of the hem, would lead to them being uncovered. When she pointed that out to the Prophet (peace and blessings of Allah be upon him), he said: “Then a cubit, but no more than that.”” (Al-Muntaqa)
Shaykh Salih Al-Fawzan (may Allah preserve him) was asked: Is it recommended or mandatory for a woman to make her dress long? Is wearing socks on the feet sufficient if the dress is shortened only so much that nothing of the calf shows? How should a woman lengthen her dress by a cubit – below the ankle or below the knee? 
He replied: 
“What is required of the Muslim woman is to cover all her body in front of men, hence she is allowed to lengthen her garment by a cubit so as to cover her feet, whereas men are forbidden to let their garments hang below their ankles. This indicates that women are required to cover all of their bodies. If a woman wears socks that is doing something extra to be more on the safe side with regard to covering, which is something good. She should also make her garment long, as described in the Hadith. And Allah is the Source of strength.” (Al-Muntaqa min Fatawa Ash-Shaykh al-Fawzan, 5/334) 
The point is that a woman’s Jilbab should be wide and come down to her ankles or more. If it is short and comes a hand span above the ankles, that is not permissible even if she covers her calves and feet with pants or socks, because that is imitating men who are enjoined to make their garments short, above the ankles. It also shows the shape and size of her feet. 
For more detail, please see the following answers: 32993 , 46529 , and 23329 .
And Allah knows best.