I have a six month old German Shepherd x Beagle Cross. For the past few months I've had her in group obedience training. There was a guy who had a beautiful five month old blue noise pitbull training along side me. Complete opposite personalities. Mine being very food motivated and his being very toy motivated.
Anyway, to biting, all puppies do this. You want to start by giving them something they will want to chew for a long time. I like to give my pup bully sticks, which are gross if you know what they are, but my pup goes nuts for them and they last for days. I also like to use Kongs. I pour a marble sized drop of peanut butter at the very end, then toss in 1-2 pieces of her kibble or a treat (e.g. boiled chicken, cooked liver, pea size bite of string cheese, etc), then I make it hard to get to by stuffing a cut carrot or doggie cookie into the whole.
Once you've address their need to chew then you need to work on appropriate ways to play with your pup. If you want your pup to learn how to wrestle and be tough, get her socialized and used to playing with other dogs her size. Avoid tug-of-war games until her manners are better. Teach her how to catch treats and soft toys, then work on her coming to you and dropping the toy in your hand.
Next, teach her what "stop biting" or "no bite" means. The way I did this was as I was playing with her, whenever she would playfully bite my hand I'd go frozen. The second she released (even if it was just to give me a weird look) I'd go into party mode, tell her good girl, and give her a "jackpot" which is where you give maybe 3-5 treats, one at a time. If you just give them a handful of treats to the pup that's one feeding and ends quickly. By slowing it down and going , heres one treat *gulp*, heres another *gulp*, etc. and making the whole thing fun she'll be more likely to stop biting the next time you freeze. After she's learned the game or around the six to tenth round, you want to start assigning a name to this trick. This is when I say "Stop Biting" and immediately freeze. Pretty soon she knows no biting. After 40 times you can stop giving treats every time and just do it randomly.
So now she knows what no biting means, but because she's in that teen phase she might still want to bite you just for the fun of it. They're dogs after all. So when this happens, you first tell her to stop, if she doesn't, then immediately end the game by walking away or removing her from the pack. A lot of trainers I know use crates and will tell their dogs "uh oh, sorry, go to bed." I just go "Hey. Stop Biting. No? 'Ganja' Timeout." Then I pick her up, walk her into the kitchen and make her stay in the corner away from everyone else. Sometimes she fights, but I don't yell or make it a big horrible thing. Its normal to have to give her a time out a few times a day, but over time her biting becomes a lot softer and is more of a tease.
You really don't want to stop biting completely. You actually want to first train her to have a soft mouth. Meaning to bite with very little or no pressure. In order to do this, initially biting lightly is tolerated, but biting hard gets timeout. Eventually biting lightly gets timeout and biting without pressure becomes acceptable. The reason for this is say one day a neighbor's little kid pulls her ear or tries to kiss her on the face. Most dogs would naturally bite to defend themselves. Well if she has a soft bite, chances are nothing is actually going to happen. It'll be more of a warning.
FYI, I'm not a trainer myself. I just been through it, watched lots of video training on you tube, read a few books, and asked a shit load of questions to my trainer.
