You were both at fault; but she was more at fault. She INVITED YOU to talk to her & ask questions and she should not have done that (IMO) seeing that you had a dog and knowing she had a dog-aggressive, dog. That was putting the two in contact (BY HER DOING) after saying NOT to. (Sort of becoming an attractive nuisance - like a swimming pool) and you may have had no idea how far apart to stand, or assumed she could HOLD the dog better than she did.
2nd Issue: IMO, since she brought the dog to a multi-dog adoption event AT a PET SUPPLY STORE (where it is common for people to bring their pets.... her dog should have been muzzled or crated but NEVER allowed the opportunity to bite or lunge at any dog or frankly with THAT ATTITUDE or lack of socialization -OR it should not have been brought to a PET STORE AT ALL! (It was probably too stressful.)
3rd: if this went to court the store (name not mentioned for lawsuit reasons) could be SUED for NOT vetting all the dogs (as dog and people friendly) before allowing the group to set up.
What if this dog had missed (in going for YOUR dog) and bitten your CHILD INSTEAD? Or what if your child (or you) had reflexively tried to protect your dog and gotten bitten? Therefore I think you need to contact the RESCUE group & point this out, and indicate this is why they should NOT bring such a dog to any other pet store event and why the PET STORE should not allow any "dog-aggressive" dogs to be brought to their store, and they need to vet all dogs in advance or make sure the groups allowed to bring dogs in, know the dogs cannot BE dog aggressive, FROM NOW ON.
My local vet school has a day where it opens & a couple of kennel & agility clubs & police groups cone and set up tables. We try to have as many different breeds as possible from the dog clubs & give some obedience & agility demos. The police do not have a table but do have to search & rescue type scent work & some minor Schutzhund games set up for the crowd to see (including the dog scaling a 6 ft wall & of course, gloved/arm attack - on command biting). They tell you over & over and all groups must sign contracts..... that the dogs BROUGHT are dog & child SAFE.