Our little rescue

Last night something horrible happend. The little rescue we have had for a year, bit our little boy. This was seemingly unprovoked. She is usually protective of him so I don't know what set her off.
We agreed when we got her if this ever happend we would find her a new home. Even though she didn't break any skin, Jonathan could have been very hurt. He is having a hard time staying away from her because he is being protective of his dog. How are we going to explain why she needs a new home?
This comes with alot of heartache because we all love her. She has come along way from the scared little girl we took out of a life of abuse.