Hi there.  The #1 way to stop any bloodshed from happening is to manage the home situation you have very carefully.  This means that you do not ever allow situations such as the ones you've described to happen. A crate, or another type of barrier, is essential in preventing fights and bites to you and your family.  There need to be 2 barriers between the dogs - always - whenever there is a potential for them to fight.  Also, it will benefit them greatly if there is a visual barrier.  Hard eyeball stares are challenging to dogs and you may not be seeing all that's going on between them, so giving them a visual break from each other is important.

Trying to "reprimand" her is, IMHO, a dangerous road to go down.  You aren't sure what her history is, and as she  is a rescue dog, the safest way to prevent this is through management as described above.  Since her old home didn't care enough to get her from the groomer's, chances are good that they didn't bother to train the dog, to teach bite inhibition, or to teach good manners in the home.  Trying to slap, smack, hit, tap, or otherwise get physical with this dog could open up a huge can of worms, considering that history.

A positive trainer will show you how to teach your dog these things.  Using positive methods will teach your new dog that you are trustworthy.  Reprimanding her will teach her that you are dangerous and unpredictable.  There are numerous online guides such as clickertraining.com and the articles on this site, but real live help in your case would be the best route to go.  Thak you for rescuing her and good luck!