ic ic.. maybe you're just being too sensitive , I'm sure your mother in law means no harm (or cursing) by saying fat and vomit.. sumtime old ppl cannot differenciate the word "fat" (which is being overweight) and "chubby" (which is just nice weight and sounds more nicer)..
and about the vomit, maybe she meant that if you never introduce solid food the baby might not get used to it and will refuse to start eating solid.
So its just a word mis-located hehe..
just take it easy i tink.. but you can explode if your mother in law would say for example, "this baby so fat or this baby surely vomit if..." now that is cursing! for me, if sumone sayingt his i'd not tink second time then scold them already haha..