How can a woman repent of an ongoing sin she is unaware of, and are its effects erased by repentance, and does Allah forgive ongoing sins?

Only those destined for perdition will perish in God's eyes. His mercy, exalted be He, encompasses all things. The questioner should turn to God Almighty and be sincere in her repentance, by regretting what has passed, abandoning sins, and having a firm resolve not to return to them.

The remedy for what the questioner complains of is clear from Ibn Al-Qayyim's words: repentance does not save one from sins unless it is comprehensive, encompassing what the servant knows and what he does not know. For what the servant does not know of his sins may be more than what he knows, and his ignorance does not exempt him from them. The Prophet, peace and blessings be upon him, used to supplicate: "O Allah, I seek refuge in You from associating partners with You knowingly, and I seek Your forgiveness for what I do not know," and he would supplicate: "O Allah, forgive me all my sins: their small and their great, their first and their last, their intentional and their accidental, their secret and their public." This generalization and comprehensiveness of repentance covers what the servant knows of his sins and what he does not know.

As for ongoing sins whose evil effects persist even after repentance, it is sufficient for such sins, along with sincere repentance, for one to strive to the best of their ability to remove the effects of their sins. God does not burden a soul beyond its capacity. And whoever repents from a sin after having committed its cause, has fulfilled what is obligatory upon him, even if its effect remains.