I think your partner maybe trying to kid herself that she can use occasionally. I think if she does it will just make her want it more, I may be wrong, and this is just my opinion.
Drugs control the person, not the other way around, which is sad but true.
Thanks for posting. If you would like to contact us at Icarus Trust may be we could help with some of the things you are dealing with. We are a charity that offers support to people having to deal with the impact of an addictive partner. if you contact us you could talk with one of our trained and very experienced people.