Is it permissible to marry a girl who had previous sexual relationships without losing her virginity, and who has shown repentance and remorse, given concerns about a repeat of such behavior, and should the mother be informed of this?

It is not permissible to inform your mother about what happened with the fiancée. Veiling her secret is obligatory, especially after her repentance. It was, in fact, obligatory for her to conceal her own secret. It is advisable not to rush into marriage with her until the sincerity of her repentance and her uprightness become clear through trustworthy individuals. If her sincerity becomes evident, then marry her, out of dutifulness to your mother. If she is not sincere, then do not marry her, especially if she committed adultery and has not repented. Do not, under any circumstances, tell your mother about the girl's situation; rather, inform her that you do not desire her and that she is not suitable for you.