I'm not sure if this qualifies as PA or simply "what the heck?"

My mother-in-law is famous for her constantly changing food fetishes. Doughnuts one day; carbs are evil the day after that; "must have pasta" the next time; "I can't eat soy"; "Oh, I ONLY eat soy..." The list goes on and on. We've gotten used to just rolling with it because generally she gives us a reason that makes some kind of sense at the time, and she gives us some warning. I hold my breath when I invite her for dinner but there is generally something that she can eat.
And then last Sunday, I invited the whole family over for dinner--nine people in total. We were putting up Christmas decorations and generally indulging in family fellowship. I said, when I invited everyone, "I'm going to order in pizza for dinner. Is everyone okay with that?" Everyone was, including MIL. In fact, she made a point of saying that she would enjoy it. (This was a week previously.) The time came last week when it was time to order dinner, because the kids were getting hungry. And THAT'S when MIL piped up, "Oh, by the way, I've decided to go gluten-free and lactose-free for a couple of weeks. I just felt like it. No, I'm not allergic. That won't be a problem, will it?"
Yeah. On
pizza. You know, the stuff that is made with a gluten-based crust and with cheese pretty much standard. Oh, yeah, that'll work. And the place in question that I order from does in fact have a gluten-free crust available, but it tastes like cardboard. (I tried it one time, out of curiosity. Yuck.) I said (and I hope that my gritted teeth didn't show), "Actually, yeah, that's kind of problematic. It's pizza. By definition, it includes gluten and lactose products. What would you like me to do about it? Shall I order one with a gluten-free crust? I warn you, it's not something I regard as a taste explosion..." And her answer? "Oh, don't worry about me. I'll just sit here and watch the rest of you eat. I'm sure I'll be all right. Even though I'm kind of hungry right now..."
I don't react well to PA behaviour--as the thread title implies, I give the PA person what he/she "wants". I ordered everything the way she said. (I did offer the gluten-free option again. She declined, in the same PA pathetic way.) And she sat there and watched us eat, making little digs about how she hoped we were enjoying the pizza, and oh, by the way, would I be angry if she helped herself to a clementine orange? Of course not, I answered. "I just wanted to make sure," she responds in a way that makes it clear that I am some sort of monster who would probably begrudge her a single orange. Ye gods.
Who does this? Who accepts an invitation a week before to a specific-food dinner and then insists that she cannot possibly eat the food in question--but doesn't bother to let the hostess know until it's time to order? Argh!!! And apart from these bizarre food quirks, she's an absolute gem of a mother-in-law. I wouldn't trade her for the world... even when she pulls this nonsense!
I'll quit ranting now.