Is it permissible for a girl to pray in trousers, and what is the obligatory Islamic dress code for prayer?

The prescribed attire for women in prayer is any clothing that covers the entire body except for the face and hands. It should be loose and flowing so as not to reveal any of her body parts. This is indicated by the Hadith of Umm Salamah (may Allah be pleased with her): "She prays in a head covering (khimar) and a full-length garment (dir') that conceals the tops of her feet," and the Hadith: "Allah does not accept the prayer of a menstruating woman except with a head covering." Scholars have differed on the ruling regarding covering the hands and feet. The majority view is that covering the hands is not obligatory, while covering the feet is obligatory.

The garment must not be thin or transparent, as evidenced by the Hadith: "Women who are clothed yet naked." It also must not be tight, as evidenced by the Hadith: "Tell her to wear a ghilalah (undergarment) underneath, for I fear it might describe the size of her bones." As for the validity of prayer in tight clothes, it is valid as long as the 'awrah (private parts) are covered, but one who prays in them commits a sin.