But your criticism of what she cooks is exactly the same - not really in the spirit of Christmas.
She's cooking what she thinks is appropriate. She's worked hard on it and you pull faces that it's too fancy. That's massively rude in its own right.
She has an idea that Christmas should be like that. That's absolutely fine.
If you want a different Christmas, you need to be aware that you are rejecting and everything she's done in the past as failing.
If you have a problem with what she cooks and buys, you have a long conversation about wanting things plainer and more to a budget if you are going to share the cost. But she's not a mind reader and you still risk upsetting her generosity of spirit.
As you say the presents are irrelevant and you are at the point of trying to score points because you clearly dislike her and the way she does things. You tend to give what you'd like to get, so keep that in mind. You clearly aren't on the same wavelength and if adding the cost of the food to your overall budget is a problem for you, adjust it! It is, after all, about the thought! All this stuff about it feeling transactional because she's asked for money, and then throwing that comment in just makes you look like you see it as a transaction anyway rather than something given with love.
You can't blame her for saying after years of hosting, please can you contribute something. Hosting really isn't just about doing a cheap shop in Tesco - it's the labour too and the clean up.
Honestly if you really don't like it, offer to host it next year for a change. Maybe she will then realise what you expectations are and you'll understand what her budget concerns are and then everyone will have a different perspective of everything in future.
It sounds a bit like you are a reverse snob and think she's 'too posh' tbh and that's ultimately the underlying problem in the whole thing, rather than anything to do with the food or the gifts.
If you want to go to hers, it's always going to be on her terms. If you want it to be on your terms, do it on your terms - which means hosting.