your MIL sounds like she is stuck in her idea that you aren't old enough to make decisions for your own kidlet

if mess is a drama, keep her on non-carpetted floors or, if your house is like our old place, put a "messy mat" underneath here. hell, you can split a garbag open and lay it under her to catch mess. mess is part of growing up! babies need to experiment. they need to learn, whether nan is ready or not, about dropping food, about eating etc.

to get around the toast thing, give her a crust off a slice of your own toast, and then rave about how much she enjoyed feeding herself...