[Ricardo]

I am going through the same thing, as soon as the leash goes on my pup starts to bite at it. You should not be afraid to give corrections as long as there is no pain to the dog it wont damage your relationship.

The one thing I would address is the martingale collar when you are not holding the leash, especially if the dog is tangling herself with the leash. Id say the choking pressure is what is aggravating your pup, try using a thick flat collar instead some thing that is more than an inch thick as it will distribute the pressure over a larger area of the pups neck.

Finally I would praise/treat the pup when you release her form being tangled so that she associates you grabbing her collar as a good thing and this should help with the nipping.

I hope that helps and enjoy the pup!