You've gone above and beyond taking care of the kid and the dog.

I'm a "single parent of a dog" and my dog (pit/lab/sumthin'/sumthin'/sumthin mix) is adopted from the pound. While she was house broken from the getgo, I've done a lot of other training/socialization. Your dog guest's problems are fear based, dogs who are very frightened will urinate. Get more frightened? They could bite. This dog sees a lot of anger, dog gets hit, kid gets slapped, your friend????

Boyfriend sounds like quite the catch too....not.

I've always used positive methods only to train Mae (my dog), lots of praise, positive reinforcement, treats when she does well or when starting to do a new behavior even *close* to it.

I don't have kids (that I know) of but I suspect this works for them too ;-)

I agree with V, doesn't sound like she is raising either the kid or the dog properly, and frightened dog with frightened kid is not good, can even be dangerous. Intimidation and fear doesn't work for either. Would she be receptive to getting help? Can you keep the dog or find someone to?