As a vegetarian who is also a picky eater (in weird ways - I eat a lot of stuff other people think is weird, like veg sushi and eggplant curry, but I hate mushrooms - which I really can't eat, as they make me literally gag - and don't like most pasta salads or cold potato salad - which everyone tries to make special for me, because they know the recipe and it's vegetarian), I say make what you want, make sure at least one reasonably filling item that she'll eat is on the menu, and provide plenty of good bread and butter (most people will eat that and it's gotten me through plenty of not-so-veg friendly meals).
My attitude is that I should take what I can eat and leave the rest alone. Nothing's stopping me from taking a big portion. And even if it's something I don't like, if someone points out that they made something that's veg so I can eat it, I still take some, making sure that the portion is as small as is reasonably polite. They don't have to see that I pick out the pasta pieces in the salad and leave the icky black olives and mushrooms. Or that I make my BF eat the stuff I don't like (possible at his family gatherings which are huge - you can't fit over 30 people at one table!). If your mom hasn't figured these techniques out by now, she really should learn them. My attitude is that it's just one meal.
OK, I have to ask - no onions?! I couldn't cook without onions and garlic. They're a basic building block of cooking! I can't stand 'em raw, but one of my fave fancy fall dishes is onion galette with mustard cream. (Deborah Madison's "Vegetarian Cooking for Everyone," which for me is the Better Homes and Gardens of veg cooking, and great if you want some really delicious vegetable recipes.)