Who Can She Uncover in front of?

A Muslimah should not uncover her adornment in front of any non-Mahrahm male. Muslimahs should especially be careful and remain covered, modest, and quiet around in-laws.

If a gay male is aware of female body parts, he should not be allowed to view a woman uncovered. And, of course, a bi-sexual male should not be allowed to view a woman without proper covering.

In addition, a Muslimah should not uncover that which she normally uncovers, in front of any non-Muslim female whom she fears may describe her to others. She may also choose to remain covered around any Muslim female whom she fears may describe her physical attributes to their husband or others.  

The Noble Qur'an – [Surah An-Nur, 24:30-31]:

“Tell the believing men to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts, etc.). That is purer for them. Verily, Allah is All-Aware of what they do.”

And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts, etc.) and not to show off their adornment except only that which is apparent (like palms of hands or one eye or both eyes for necessity to see the way, or outer dress like veil, gloves, head-cover, apron, etc.), and to draw their veils all over Juyubihinna (i.e. their bodies, faces, necks and bosoms, etc.) and not to reveal their adornment except to their husbands, their fathers, their husband's fathers, their sons, their husband's sons, their brothers or their brother's sons, or their sister's sons, or their (Muslim) women (i.e. their sisters in Islam), or the (female) slaves whom their right hands possess, or old male servants who lack vigour, or small children who have no sense of the shame of sex. And let them not stamp their feet so as to reveal what they hide of their adornment. And all of you beg Allah to forgive you all, O believers, that you may be successful.

Hadith – Bukhari 7:167:

The Prophet said, "A woman should not look at or touch another woman to describe her to her husband in such a way as if he was actually looking at her."

Hadith - Muslim, narrated Aisha (radhyAllahu ‘anha):

“A eunuch used to come to the wives of Allah's Apostle and they did not find anything objectionable in his visit considering him to be a male without any sexual desire. Allah's Apostle one day came as he was sitting with some of his wives and he was busy in describing the bodily characteristics of a lady and saying: As she comes in front four folds appear on her front side and as she turns her back eight folds appear on the back side. Thereupon Allah's Apostle said: “I see that he knows these things; do not, therefore, allow him to enter.” She (Aisha) said: Then they began to observe veil from him.  

Hadith - Al-Tirmidhi 3109, narrated Abdullah ibn Mas'ud [Tirmidhi transmitted it.]:

 The Prophet said, "A woman should be concealed, for when she goes out the devil looks at her."  

Muslimahs should not socialize with non-mahram men, and should only speak out of necessity to non-mahram men. Allah (Subhanahu wa Ta’ala) knew that mankind would be tempted to let their guard down and their Hijaab down, around in-laws. Surely Allah (Subhanahu wa Ta’ala) is All Merciful to provide us the guidance we need in every aspect of our lives. In reference to socializing with in-laws, such close relations can easily lead to adultery which has the death penalty.  

Hadith - Bukhari and Muslim:

The Prophet said, "The in-laws are death."