My girl is also biting all the time, but when I say NO, she will instantly stops.
Basically I told her 3 times NO. She didn't listen. So I bite her back on the back of her neck. Until she whined (GSD are cry babies, so it didn't take any real pressure).
Four days later she stopped listening again. She was like, was that an coincidence? I can stop listening? He really didn't mean it, right? So I have bitten her again. Since then she has a great respect for the NO.
I'm not fan of physical punishments, but I wanted to make clear for the future, that NO is the line that she can't cross. And it's working perfectly.
//I'm not an expert. Just a thing, that worked for us.