Oh my goodness I am so sorry this happened to you and your baby.
You have every right to be angry. I cannot believe they would walk away and leave her on the grooming table!! Maybe its just me but I feel like Petsmart & Petco will hire any warm body to work in the grooming and doggy daycare areas with no regard to safety.
I would definitely file a complaint with the store manager and possibly higher up. Granted it was an honest mistake, like you said, its the most basic grooming rule that you do not leave a dog unattended.
Stories like these are so disappointing. She is very lucky you were there to be her guardian angel.