ANSWER:
This depends on a number of factors:
1.Does she have a better alternative or after divorce she will regret it because she can’t afford to survive financially or is unable to find anyone else to marry her and fulfil her needs as a human being.
2.Is her Iman increasing, decreasing or is it status quo! If it is decreasing, she must not stay as she must not compromise her own Iman. But if her iman is intact, she should try and give him advice and dawah and remind him of Allah.
3.If he is still Muslim and not left the fold of Islam. If he doesn’t pray at all, you shouldn’t stay with him.