You're girl's still only a baby, so it may take her a while to settle to handling especially if she wasn't used to it before she came to you. Patience and persistence are keys. Taming and reducing nipping isn't a quick fix as the hamster has to learn to trust you.
If they're territorial in their cages, I use something to transfer them out, e.g. exercise ball, tube. As other posters have said, make sure your hands are clean with no food smells on them. If they're bite/nip when they're being handled I let them know that this is not acceptable (e.g. a firm no). I also make sure they aren't put straight back in their cage, otherwise they learn that biting=going back in cage. Mine stay out until they're well behaved after a nip. Oh, and they also get a lecture about good manners, but I think that's more for my benefit than theirs
Try not to show fear or be nervous when handling, as they seem to pick up on this. Recently I was handling the chinese hamsters I have living in a stack of bin cages. I have a particular female who has become rather moody with age and tends to give a mean nip. I reached in to get out the little young normal boy and picked him up with no problem. We had a lovely snuggle, so imagine my surprise when I looked underneath and saw 'he' was a she! I'd gone into the wrong cage and picked up my evil girl instead, but I'd done it so confidently and calmly she'd not nipped!