Lindsey,
This may sound brutal, but I have to ask you this. When you say "I can't do this", have you given up? If so, that's fine, contact the breeder and see if they will take her back. No need to prolong the agony if you've decided it's hopeless.
If you really want help with this, reread Princess Zoe's post. That's exactly how her biting should be handled if she's biting you hard enought that it hurts. If she's just mouthing you (lightly chewing on you), simply substitute a toy or some rawhide.
If she bites you everytime you get on the floor, DON'T GET ON THE FLOOR! There's no reason why you can't play with her while sitting in a chair.
I'm not surprised that yelling, tapping her on the nose, or biting her back
didn't work. She acted aggressively, then you acted aggressively. She thought you were playing a fun game.
The way to stop this is to teach her that bite me = loss of attention. It will take MANY repetitions.
Hitting a Yorkie (even "out of love") is abuse. Period.