I don't want to sound harsh but this was due to feeding error on your part.
First off, you should never need to interfere with feeding. By doing so, she uncoiled because of your interference and that very well could be how the rat got the upper hand. BPs are very good at doing what they do and if they bite and coil, they get the job done even if the rat struggles.
Now the one exception to this is if you tried feeding a rat that was too large for her to handle, which I don't know the specifics of this situation but it sounds like that could of been the issue in the first place.
I don't have the feeding chart handy but look it up and make sure you're feeding the right size prey. Give her a week to rest and recover and then you can try feeding her again. Don't stun the prey, either kill it and then if she takes it, next time you can try to get her to switch to frozen thawed or continue to feed live but with the right size prey and let her do her thing. Getting a scratch or bite is unfortunately part of feeding live. Usually if feeding the correct size prey, this is rarely a problem, it is part of feeding live and by interfering you're only going to do more harm than good.
Good luck with your next attempt, I hope things go smoother for you.