Dear Jaime---you saved that puppy, and that puppy is jealous over your baby. Isn't there something you can do to make you Yuki feel extra special around the baby too? When I had my first baby--my parti-poodle was protective, and when my baby was on the floor on a blanket, she had an instinct not to go on the blanket---not even the edge..she was careful--then all of a sudden she started not to be able to jump on the couch, would walk into walls----I asked the vet, if her eyes were getting worse (lack of vitamin something when she was born that made her one eye looking like cataracts)--the vet said no and that she could be jealous over the baby--feeling less loved. So, I paid attention to her more, and she slowly got back to her own self--not quite perfect but better....she didn't come to me as the same as before having the baby. So...give it a try a little longer---even walking the dog along with the baby in stroller...if that doesn't work--at least you know in your heart that you've tried your best and you must think of your baby and find another loving home just like you described.
I have done daycare, and some young kids were brutal with my maltese. One little boy kept putting a choke hold on my dog. I had to eventually tell the boys parents to talk to him about this, because he wasnt stopping. Other kids poke their eyes....give the dog a chance, if you are that worried for your child, okay, but you cant always blame the dog or say it is mentally not all there. Thats not fair. And it is a bichon mix, with all this overbreeding and stuff, some dogs dont have good tempermants, but that is the breeders fault, not theirs.
have u considered that not to blame on son but maybe when not looking is getting a bit rough playing with her maybe hurting her and thats why all of a sudden she is biting i have seen it happen little ones dont know any better and play a bit rough with the pet maybe watch and see if that is happen if it is work on the problem with your son and teach her to trust again. just a suggestion dont know am not there