Wow! I'm so sorry this happened to your baby
In my opinion, there is NO excuse for this happening, it was a preventable accident. If she was taking proper care of your baby, she would not have let her 8 year old put gum on his hair, Or she should not have left him alone with your furbaby
And she should have called you to ask what to do when the gum was in there. Thankfully, his hair will grow back, and it is a blessing that nothing worse happened.
Hoping you find a better sitter that you can trust. Have you thought of having a family member stay at your house with your baby when you are gone for awhile?