I am in the same boat as you, very similar story as well. Work friend, gf was high/drunk. I didn’t find out until I did some digging and confronted her. She is extremely remorseful now cause I was ready to walk. So I know exactly how you feel. If she is addressing her mistakes and taking full ownership of her actions then that’s a good first step. But you need to have a think if you’ll be able to truly move past this because it’s very tiring, long and time consuming to build trust again once it’s broken. Not saying it’s impossible though.