MIL issues

So I live with my in-laws and have been having a lot of issues with my MIL not respecting boundaries and not respecting me as a mother. Anyways, I want to know if I over reacted to this situation... My LO is 2 months old and just got her shots on Thursday so she doesn't have immunity yet. My husband's cousin came over but told me she was sick so she was going to stay away from me and the baby. She then proceeds to tell me how she's been sick since Monday and got sent home from work yesterday because she was so sick and is going to go to urgent care today. Then my MIL comes downstairs and touches the cousin's face to check her temperature. A minute or so later she goes to touch my baby without washing her hands. I quickly moved out of the way with the baby and told my MIL not to touch the baby after just having touched the cousin's face. She looked at me like I was crazy and proceeded to tell me that the baby has to get exposed to germs at some point. I am not a clean freak and know she needs to be exposed but I also don't feel like sitting in the ER at 2am with her if it can be avoided. I'm pretty pissed that she doesn't care about what I think is best for my baby and is trying to tell me how to parent. Am I over reacting?