She means it playfully, but it is actually starting to hurt. I have tried the simple "no, sit" technique, and reprimanding her but she doesn't stop. Help!
I find that redirecting is the best course of action. Substitute your arm for a toy or bone. Also, stop playing with her. If you continue even when she is hurting you, she will think that the roughness of her play is okay. If you stop, she will know she can't be too rough, otherwise playtime is over.
I agree with Paige. In basic dog training, the instructor will advise/demonstrate that you immediately cross your arms in front of your chest and turn your back to the dog, thus giving the dog No attention at all. Sometimes dogs perceive even negative attention as better than none, which is possibly why giving her commands isn't working (if she already knows them). When the dog is calm, you can turn around and continue to interact. This may take many turns as the dog learns what is appropriate.
sour apple spray on your hands or where they bite?
I watched a Dachsund over the weekend who wanted to playfully naw on my fingers while we were playing. I think the owner doesn't mind, but I did. He also wanted to bark at me when I wasn't giving him my direct attention. I agree with Paige about redirection; playing with a soft toy at the same time as you are playing with the puppy will allow the fun to still occur. The puppy/dog will then transfer some of that energy to playing by himself with the toy, giving you a chance to breathe. :) I also agree with Deb about turning your back on the negative energy; waiting for calm behavior is key.
For the barking issue, twice I put him outside of the room and closed the door when he did not stop barking with my simple command. He waiting patiently outside the door with just slight whimpering. I did not keep him out long and then started fresh when he returned into the room, realizing he and I were both in training. (One of these bark sessions was for a simple phone call with my dad!)
A dog can not begin to believe that he is in charge, it will drive him to some very bad habits. Be assertive and know what behaviors you accept and will not tolerate, then communicate these simply to the puppy/dog you are watching. A dog wants nothing more than to please you as his/her caregiver.
You can always use a spray bottle with water. Telling the dog No first than if she doesn't listen you spray her. She should stop the behavior than you want to make sure and reward her for behaving and listening.
"good no bite, good girl" (when she stops what you asked her to do.) You always want to end on a positive.
You do want to make sure you talk to the parents first and let them know that this is the issue that you are having, see how they normally handle the situation when they are at home.If they don't have a way you can always mention to them about using a spray bottle.