Can you start by giving us some stats on your g/f? How long training? What are her goals? What does she expect from "trying some juice"? What is her current diet? Remind her that "juice" ain't a magic pill if she doesn't have a serious diet & training regimen already in place.
If you must give her an answer, probably anavar is the best because of the very limited & relatively predictable side effects. But still, its all just a waste if she has unrealistic goals (juice for girls isn't the same as juice for guys) and her diet & training aren't already well established.