Foster dog aggressive toward non-family members?

Hello,

I have been fostering dogs for about a year now, and we often get the "harder to handle" dogs. The current dog we have is a terrier mix and she is about 15 pounds. She is very sweet with me and my husband and loves to play and cuddle. The problem is around other people. We have taken her on two home visits (at the rescue's request) and to an adoption event. She's awful. She will bark, growl, bite and try to attack all other people. She has bit 6 people (one hard enough to break the skin a little bit). I don't think she is being defensive of me or my husband, because her actions are the same whether we are her at the time or not. She is okay when we are on walks and someone is in their yard or walking across the street.

We've had other dogs who showed signs of aggression (mostly fear aggression), but this a trickier situation to work with because she shows no signs of aggression with us; it's hard to fix something that we don't experience regularly. The rescue suggested taking her to populated places, like PetSmart and downtown, to desensitize her. I feel like this is not a good idea. I can't control EVERYONE who just thinks they can pet her, no matter how vigilant. I don't want a curious three year old to be attacked by this dog, and I also don't want to be held liable for this dog since she would be in my possession when we are "out and about".

Any suggestions on how to work with a dog who is is bitey toward basically everybody?

Thank you!