sgirl, I can empathize a bit, my MIL did this to me a few weeks ago...actually I kinda found it quite rude (JMHO), she's known for a long time what I deal with and go through, and then was insulted when I couldn't eat a thing placed before me...I mean, c'mon, why even bother inviting me? I felt really, really hurt, so I can kinda understand...BTW, my DH is an only child...so it's not like there are a whole lot of people to cater to..
I host Thanksgiving at my house every year, so I ask, and people know what I'm serving...also like if I invite my friend over who is vegetarian, I don't decide to make steak...it's just rude...really, don't your inlaws know what is going on? I'm urging for you...just saying...