Autumn you might not think spaghetti hoops were a treat, but your MIL may have thought it was perfect for a little child- in the UK that would be considered a child's food. I have eaten all kinds of awful cultural delicacies in my time, from snails to veal's brains, which for that particular culture were really important and the people wanted me to eat them, and I felt awful that I couldn't enjoy them. I think, in the nicest possible way, you need to get over this feeling your way is better and right and start to see that some of the things you eat might not be that delicious either (cheese pastries I find disgusting for example, but they are eaten all over Eastern Europe). I woud not give my child a cheese pastry concoction as a 'treat', but I don't think myself above it if my MIL produces them as a 'treat' for us, and we do our best to be polite and express pleasure, not sniff or turn our noses up (because I think your hostile attitude will be leaking out all over the place even if you do not directly say anything, body language will do the talking).
I also worry that you are basically training your child to look down on the host culture by dismissing the food, this is NOT a good position to take. Try to start seeing it as 'difference' rather than 'better/worse' otherwise you will drive yourself bonkers, and your child will end up having to agree with you to pacify you and to support your cultural identity, and that's not a good thing to put on your child, who, if growing up in the UK may have a strong British identity as well as her original identity (children are infinitely more flexible than adults).
Finally, yes, my husband is VERY straight talking, but over the years we have got along with a few misunderstandings, admittedly. I like his straight-talking sometimes, other times I find it quite rude, so you have to remember that there is no one right way to be- often British people have a very convoluted way of explaining things and use euphemisms all the time, but I don't think this is a bad thing, I have seen the bad side of plain talking in my husband's family and there is often a lot of drama and trouble because of it.
Is your husband from the UK or are you all from your home country over here?