What should a girl do who wishes to wear modest clothing or the niqab, but her mother prevents her and damages her clothes, especially since the girl is studying medicine and fears her mother's reaction if she hides the rest of her immodest clothes, and finds no support from anyone in her family?

It is not permissible to obey one's mother in going out in immodest or tight clothing. One must maintain the modest, covering Islamic dress that conceals adornments and does not reveal physical attractions. You should gently discuss this with your mother and explain that this dress is a divine command. Seek assistance from righteous women who can speak with her, while continuing to treat her kindly, dutifully, and praying for her. It is not permissible to go out to university or elsewhere except in Islamic dress, and rely on Allah, who suffices and provides a way out, in accordance with His (the Almighty's) saying: "And whoever fears Allah – He will make for him a way out And will provide for him from where he does not expect. And whoever relies upon Allah – then He is sufficient for him." (At-Talaq: 2-3).