How do you guys feel about my MIL doing this?

Whenever we bring my son over to MIL she always tries to take off his diaper to let him “breath” In the summer in her front yard she wanted to and I said “no he’s fine” and she’s like “you want to be out of your diaper, tell mommy that” and stuff like that. How would you guys deal with that? She always does the comments like “tell her you want to be left alone” and it annoys the f out of me.

Edit- a lot of you guys are saying that going diaper free is okay.. Obviously I know that but I let him go diaper free on my time at my home. Not somewhere where we only go to once a month. There’s no reason for that. It’s not like we NEED to have him diaper free the one time he’s at grandmas.