
I've found the best way to stop nipping/mouthing is to use a combination of methods.
1. Don't allow her to get over-excited in the first place because that's a sure trigger for nipping.
2. If she has squeaky toys then squealing will only wind her up, so don't do it.
3. When she gets mouthy say calmly and quietly "No, gently" and give her one of her toys, shaking it so that she starts ragging it; saying "Good girl" now will teach her that ragging her toys is allowed!
4. If she's become hyper despite your best efforts to lower the household excitement levels then either carry her, without a word, to her playpen for 'time out' or if she's already in a safe place simply leave the room for a couple of minutes.