I haven't had had a chance to read every single comment, but I didi read where you said that the aggression incident occurred as your son was trying to get her out of her kennel. This is an incredibly dangerous thing to do with a dog you don't know well. A dog's kennel needs to be a sanctuary...
I couldn't get my son to go to sleep in his room by himself until I started letting one of the dogs sleep in there to "protect him". Once he had a dog at the foot of the bed there was no more getting out of bed after bedtime and no more nightmares. Not to mention, there is nothing sweeter than...