The best thing to do to stop nipping and mouthing is to let out a puppy like yelp, this immediately makes the puppy back away as it is what her litter mates would do. Its a way to let them know that it hurts. They won't understand all the no's and putting them in another room etc. When they nip, you yelp then turn your back on them (get visitors to do the same) they will soon get the message of 'ouch that hurts and i am not playing because of it' Try this link for a full guide. Hope this helps :D