My mother in law vs us as parents

I currently live with my mother in law and when my baby was around 2-4 months old she had a fit that he only had a diaper on. I did have a blanket over him and he was in his snuggleme. We were going to ignore her persistent request to put a onesie on him but she left the room, and came back saying we were completely defiling her (ignoring her and acting like she doesn’t know better because she raised 3 boys herself. I married her son CLEARLY, and he’s 21 now.) So we put a onesie on him. She ALWAYS says “that’s a baby, you can’t do him like we do ourselves. He’s small” But for this particular incident- people do it ALL THE TIME. He was covered in a blanket so I don’t see what the problem is. She claims the baby can get sick “from being in this air with nothing on” but I don’t think that’s how it works. It was about 80ish degrees in the house. The baby was fine and comfortable. I’ve wanted to be a pediatrician most of my life and I don’t remember seeing anything about a baby becoming sick that way unless it’s too cold in the house.

My baby is now 7 months but I’m currently pregnant again. I don’t want her having a heavy tone with this baby like she did with the first one, Can a baby really get sick by having a just a diaper on, but being covered up in a blanket?

*NO RUDE COMMENTS PLEASE*