How can a woman overcome her despair and frustration due to instability in her marital life and its impact on her religious commitment, especially since she links the improvement of her religious affairs to psychological stability?

The anxiety and depression you feel are due to being distant from Allah. Therefore, hasten to repent to Him, the Exalted, and fulfill your obligations such as the hijab and prayer, and beware of your self that incites evil. Repentance is obligatory immediately, and delaying it is a sin. Draw closer to Allah through acts of obedience and supererogatory deeds, read the Qur'an with contemplation, increase your remembrance of Allah, ask Allah for steadfastness, keep company with righteous women, listen to religious tapes, and beware of Satan making you despair of Allah's mercy.