biting/mouthing.batking

Heidi is approximatley 12 weeks old. She's very smart and learns quickly. One problem we have with her, however, is that she likes to mouth/play bite with us. It doesn't feel like play biting, but I know it is.How do I get her to break this habit. At her age, it is a bit of a problem due to sharp little puppy teeth, that's why I wish to end this NOW, before she is big and can do real harm. As well, when I repremand her, she talks back! Sassy little thing she is.  I would like to break her of this too., Other than that she is great. I taught her, sit, up  pretty, high five, shake, down down, crawl amd now working on stay amd roll over. So, she is very smart.. just bossy. The thing that gets me is that she sees me as the alpha, yet still gets out of  hand. Im afaid someone might get bitten. Thank-you,