I totally understand how hard letting go is. Like you, I have known many addicts in my life. I partied hard with them, was good friends with them, dated them, and then when I got pregnant with my daughter I cut ties with it all. Including cutting ties with my daughter's father because he was an addict. Coke, crack, ketamine, heroin, etc. He WANTED her, too. I remember being at his new place after my first sonogram... He was making his roommates watch it and he was talking about getting a crib, how we needed to take a trip to see his mom, etc... and I looked around and all I could think was - what if you have her and the cops come or you can't stay sober while she's here or your roommates can't and something happens to her. I left that day and never looked back because he had no intention of getting clean to be the amazing father I honestly think he would have been. And never, in a million years, did I think I'd end up in a relationship with a recovering addict 12 years later.
You have to decide what is best for you. What your limits are. What you can handle. You obviously have experience with addiction and know what you and she are up against. and you obviously care about her. Just don't forget that the only help you can truly provide is support in her recovery. Anything else is just aiding her addiction.