OK.... Sorry you are doing it so tough and that she is a bit of a wild child. I am a behaviour trainer and this is what I get a lot of. Dogs that people give up on
It takes time and time is not days, but weeks and sometimes months....
Firstly I do most of my training for bitey dogs with luring off.... No you are not rewarding the nipping, you are teaching the "off"
The dogs goes to nip, you hardly move where the dog is nipping, but with your other hand you have an awesome treat and get to that nose and when the nose follows the awesome treat you say "off"... It means you have to carry treat the whole time and if you have other family members they have to do the same.... Now you are trying to get to you saying "off" when the dog moves towards you and rewarding the actual dog not biting you... this takes time and also timing.... I had the puppy from hell myself as she was a singleton, no littermates to teach her about mouthy ness... everything that moved was fair came.
So dogs mouth goes toward whatever part of you .... get the treat out towards the nose, it has to be good, as the dog moves away from you say "off" and as soon as you find the dog following the treat instead of going to bite, say a happy "yesssss" and throw that treat or if the dog is gentle feed the treat out of your hand
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The more you do this and it will be done often, you will get to the bit where you say "off" when you see the dog going to nip/bite and you say "off" and don't even need a lure, Again say a happy "yesssss" and reward.... I give a couple of quick treats when they do it the first few times without luring as they have to know they did well..... Luring is putting a treat in front of the nose and getting the dog to follow it in the direction you want.
I love lure training and clicker training combo as dogs get it... it is uncomplicated for them.
You have to do lots of it.... often and stay pleasant and happy.
When you gat angry and frustrated or even yell, things get worse.... Same as time out.... a lot of people do time out but yell at the dog. A Dog time out means say nothing either put the dog away ( best if you leave a open ended leash on ) and say nothing, do not interact, even when they get let out.... It is the total ignore that is the dog language of you were bad. If you talk they are thinking that they are still engaging with you... silence is best for the dog