This. Absolutely.
She probably thinks of you as family @Happbee.
I know that I do with my DC's partners/spouses. They all get treated as near as dammit possible, in exactly the same way as those I gave birth to. I love them so much, and before reading Mumsnet AIBU threads, I would have expected them to understand that I was asking them for a favour because I really enjoyed their 'cooking' - in this particular case. I would ask that of my daughter - if she could make such tasty desserts - and would not think it was any different to ask my DiL for the same favour.
Maybe in future I should go down on my knees, put my hands together, and say
"Please my most blessed DiL, would you do me the massive favour of making me one of your delicious Tiramasu's, as I am having FiL's brother and wife over for supper on Wednesday, and when I mentioned your wonderful pudding to them they almost drooled. Of course Dad and I will pay for the very expensive ingredients and for any electricity used, and of course we will pay you top dollar for your time. You are of course very welcome to come as well, but then you must know by now that you are always welcome, no invitations necessary. However, I do think I should warn you that my dear BiL isn't exactly the most scintillating company, and his dear wife always brings her crochet with her, even doing it and talking about it throughout any meals at the dinner table - in fact I'm surprised she didn't bring it to your Wedding reception..."
I noticed OP that she did ask your DH if he wanted to go. Unfortunately (IMO), one of the few things wrong with the English language is that unlike many other Latin based languages we don't have a plural 'you', so if your MiL said to her dear son "would you like to come, she almost certainly meant both of you(s)!"
NB I mean this light-heartedly, no serious sarcasm meant - which is just as well as I am not very good at it!
NB2 - to anyone reading this: I know that the English Language is not solely a Latin based language. There is also a large ancient Greek influence, some norse, some Indian, we also adopted a few of Shakespears made up words, and there might even be some double Dutch for all I know.
It really is time I was asleep, so sleep tight, and don't let those pesky mainland European bed bugs bite.