Quoting MommyToWesley:" You don't know that her buying a winter coat is insinuating that you can't afford one. She just thinks ... [snip!] ... You should just put a winter coat on over the straps, backwards with her arms in the sleeves. Or at least put a blanket on her."
DD was wrapped in a fleece blanket also.
MIL didn't directly come out and say that she thinks we can't afford one but her facial expressions and remarks as I was explaining why DD didn't have a winter coat on pretty much indicated that. Almost like she thought I was just talking out of my ass because I didn't want to buy her one.