3 months is definitely still in the normal puppy age of biting like crazy. So don't think you're doing anything wrong. Just be as consistent as you can with disengaging when bitten, and praising her when she bites her toys like she's supposed to. It can be tough with kids if they are not consistent with it like you are, and thus confusing the dog. But our pups I think stopped with the biting around 4-5 months