ouch, painful. My empathies go out to you, that’s really hard to go through.
From what i’m understanding, you know why she suddenly dropped you, and acknowledge you were in the wrong. You very likely need to give it some time for her pain to lessen. Time heals, it’s a concept from Torah. Dont try doing anything while the wound is fresh. Work on yourself in whatever this mistake was in, work hard to change it. It’s self-improvement and it’s showing you are serious about changing, showing you’re committed to not repeating such a mistake. After that, apologize. Without excuses or justification. Just a true heartfelt apology. And i’d strongly suggest speaking to her mother at that point too, perhaps even before her. Apologize, tell her you know you were wrong, that (and how) you worked on changing. It’s painful, but i can’t guarantee she’ll accept you back even then. I hope she will, but realize she was hurt. At the least, the apology will be accepted, she won’t be upset anymore. But she might be hesitant to get close to the same degree again, or to get close at all… Hope and pray for the best, but know a scar from a wound may remain though the wound healed.
It’s hard, it hurts. Been there, done that. I hope it all turns out for the best n with the least amount of pain. If it doesn’t, know more people will soon come and fill that void. All the best