My Maggie was home just a few weeks when she bit my DS on the face. He was just walking by her while she was awake on the sofa - not looking at her, not touching her, not gesturing to her - and he got bit. My DH was ready to send her back. But I realized the situation was my fault - I gave her far too much privilege and latitude. Revoking furniture lounging, touching her while she was on her bed, hanging on her, etc. stopped right away. Now she needs permission to get up on the couch (although it's anything goes when we're not home.
You're lucky that she'll give a warning growl. It sounds like you're doing all the right stuff. So glad your son and Sherry have made up!