Part of dealing with a parent like this is knowing that you are doing nothing wrong and sticking up for that. If she asks about the menu refer her to what is on the wall - ie post your menu for her to go look at. If she doesn't like it not your problem as you have offered her the option of bringing alternate foods. Part of accepting our home for their child is that they have to accept all of it so that means there will be days when things aren't 100% anything - this is a home afterall and things happen.
I get what you mean by her tone of voice. It's like being the witness in court - you have done nothing wrong but you are being badgered by the accussed's lawyer. You do not deserve that and do not have to tolerate that. She is treating you like the fired nanny and that you are not. I might even put it that way saying something like I'm sorry but I am getting really offended each night you pick up as if I have not done the best for your child. If you are truly unhappy then you should take him somewhere else and see what she says.
In reality she is probably just suffering from a severe case of mother guilt and again bring it to her attention and let her know that while you don't mind sharing about his day you are not willing to do a play by play but will give highlights only. Tell her that is normal. Let her know that she is still a good mother even if she doesn't know how many spoonfuls of peas the child ate at lunch or what time of day he pooped. All she needs to know is that he ate well and did have a poop. Details can't matter because there are too many children to deal with.