Hi and welcome Bkcdragon1976
I understand your concerns. I've never done hard drugs but for me I need to be abstinent from everything like that to feel like I'm safe in recovery.
On the other hand, whatever happened in your last marriage has you skittish and thats understandable...but history doesn't always repeat - and there are many many cases of people who clean up and never do their drug of choice again.
I'm also not sure how long your gf has been clean.
The thing is you're the one out of all of us who knows this woman best.
I wish I had a guarantee for you either way but addicts aren't monolithic - we share a common problem but we're all different.
How much have you discussed your concerns with her?