I am only clean 13 days, so I'm no expert, but it is my 3rd time cleaning myself up. Hopefully the last.
The number one thing for myself was a strong desire to quit.

Does she have a reason to quit? That can be very beneficial. At least it was in my case.
Be patient, and don't blame her or make her wrong. She is probably already feeling like a failure for her perceived lack of control or ability to quit.

If you want to help and have the finances, offer some fantastic reward that may motivate her. Do I hear vacation to some tropical paradise? Just kidding. Has she ever wanted you to do something with her that you just haven't wanted to do? Dancing? Really nice dinner out? Offer to do something for her that is all about her. Pay for a massage, manicure, pedicure. Haircut at a very expensive salon.

These are just ideas. You know what would be enticing to her. They don't have to be expensive. You could offer up 5 one hour foot massages divvied up one per week as long as she stays clean.

I give you kudos for wanting to support/help your gf. I would have loved to have that support.