MIL not cooperating with baby name.

My husband and I haven't talked to my MIL in months. Well today she just happened to be in our town and we ran into her at Walmart. She has me blocked on fb, etc. Anyway she's all rubbing on my belly asking what name we're going with and after we answer she's like. Well I'm gonna call him by his middle name. Like no, if I wanted him called by his middle name I would've made it his first name and I'm not trying to make him confused. Suggestions on how to address that?