One thing you can do is stop all play and completely ignore your dog when she nips. For dogs (like kids!) any attention--even negative attention--will cause them to do whatever they did to get attention in the first place. Another thing I did with my dog (who used to nip during play, too) was to put her in time outs. She would have to do in the kitchen with the door blocked by a baby gate without any attention for a couple minutes every time she nipped. Others recommend saying "Ouch!" and putting a toy in the dog's mouth (instead of your hand), but my concern is that this might reinforce the nipping (with the dog thinking, oh if I nip I get a toy), so I just stop all games and ignore my dog if she gets too nippy.
Good luck!