Babysitting

My boyfriend's mom has been wanting to babysit our 7 month old son, but I'm just not comfortable with it. I don't even really like leaving him alone with my mom. I would be a lot more comfortable doing so when he is older. I don't want to seem rude, but I just really don't want her alone with him. Where he goes, I go. My boyfriend thinks that I should let her watch him, and no one seems to understand or even care about how I feel about the situation. Should I let her babysit or just tell her no?