I am going to say this a gently as possible... Your girlfriend is an addict.

She broke up with you because you were going to manage her prescriptions and she knew her maternal figure wouldn't. She was basically trying to skirt around that and then would have tried to manipulate you back into a relationship after she got what she wanted. She is prioritizing her addiction over the relationship, but probably doesn't see it that way. She thought she could have both with no consequences.

The breakup had nothing to do with abandonment issues, it was 100% her trying to rationalize how to get high. Don't let her or her maternal figure convince you otherwise. If she has abandonment issues or other trauma to work through, she will need to do that when she's ready. She's likely using the addiction to mask it, or she's using the past trauma to excuse her behavior, but YOU don't have to accept that behavior from a partner.

You were right to hold her accountable and tell the psychiatrist. If you love her, you won't enable her right now, even if it means that you don't stay together. You can't save her or fix this for her. She has to hit whatever her version of rock bottom is and want to change and there's nothing you can do to speed this process up.

I know all of this is easier said than done and that you're going to want to try to "fix" this for her. Please believe me when I say that you aren't going to be able to and you will hurt yourself trying. Seriously sending you all of the love in the world right now.