How can I remain steadfast on the path of righteousness after a period of deviation, and what is the effective way to advise my fiancée who is negligent in her prayers?

Among the most important things that keep a Muslim steadfast are: striving in the pursuit of knowledge and acting upon it, associating with righteous people, attending gatherings of remembrance (dhikr), and making abundant supplications (du'a). Beneficial books in this regard include: Mukhtasar Minhaj al-Qasidin, and the books of Ibn al-Qayyim and Ibn Rajab.

As for the fiancée, she must maintain her prayers, because abandoning them is one of the greatest sins. She should also be diligent in supplication, associate with righteous women, engage frequently in remembrance, and seek knowledge.

It is important to note that the fiancée is a non-mahram to her fiancé until the marriage contract is concluded. Therefore, it is not permissible for him to speak with her except out of necessity.