It is very stressful for a dog in a shelter but also they do the tests to get a good idea on what the temperament and such is like. Also if the said she had mild aggression in a stressful environment what would happen when she was more comfortable. She could either not have the aggression or it could get worse... just my opinion.
I have a couple questions for you, do you want to find out if her aggression would happen to get worse with the little dog that lives with you now? Do you know how to properly stop a dog attack if she did attack your dog? Do you have the money for a trip to the emergency vets if an attack did happen?
I am not saying not to adopt her but if there is a question about your safety or your dogs safety I think I would look at a different dog.

I do love pitties.
I also think with proper training a lot of dogs can be helped but I also think a professional would be your best bet.
Again this is only my opinion.