What can I do about this without confrontation

If you enjoy her company and are happy for her to come along then just say next year everyone will be making a contribution and would she be happy to bring wine/cake or whatever.

If you don’t enjoy her coming then tell her it’s a family only event in 2022.

Has she family to go to at Christmas? How did she drift into being part of your Christmas day?
I agree that the best thing would be to say that you've decided to all contribute towards the cost next year so would she mind bringing x, y and z.

Your friend is taking you for granted.
I agree with others that you should tell her family only for Christmas but to sweeten it you could say she is welcome to drop in for coffee and mince pie between Christmas and New Year.
Her response will tell you how good a friend she is.

I think you missed a trick - for the last 2 Christmases you could have cited Covid regulations/caution to reduce the number of people getting together, thus leaving said 'friend' out.

What you do now depends on whether you mind her coming or not. There are plenty of good suggestions above for asking her not to come or to make a contribution.

is she REALLY a friend? If you don't want her then say no when she assks.

I would tell her now that next Christmas you are keeping your celebrations on Christmas and Boxing Day for family only. Get it out of the way now rather than having the thought of it hanging over you. Make sure she understands so that there is no misunderstanding. Also at some point throughout the year I would bring it up maybe asking her what plans she has for the festivities.
Agree with others she is taking the p*

Is she a good friend for the rest of the year?
She probably doesn’t get that she isn’t welcome, she’ll just think that ‘she’s one of the family’. Perhaps she shouldn’t but she has been made welcome, I presume. So she just presumes.
All families have members who are a bit mean or lazy or just don’t quite get it.
Only you know the background story but before you exclude her (if that’s what you want to do) just question how you will feel next Christmas. Relieved or guilty? If it’s guilty then will it spoil your enjoyment?
You’ve got plenty of time to make a plan.

It’s impossible to give a view without knowing if it’s her presence, failure to make any contribution, self-invitation or expectation of a certain level of goodies which is annoying you, how this started and how it’s gone on for so long. Explain please!

Come the beginning of November, drop her a letter keeping it very simple. "You are making arrangements with x and y this year. We know you will understand and hope you will be able to celebrate without us. Maybe we can meet up for tea sometime in the New Year."

Don't complicate it - simple and brief works best.

Do you want her to offer money/bring something or to not come?

If the former I would bring up the subject now, saying money is tight so next year she would have to contribute, tell her we are splitting the cost next year so if she is coming would have to pay whatever amount.

If you just don’t want her there it is going to be very difficult to come up with a reason, hopefully, the cost of contributing would put her off.

Whatever you do I would talk about it now whilst it is relevant and occasionally during the year to reinforce it.

So you’ve had 30 yrs without confrontation !

Just tell her that you’ve, as a family, your arrangements for next Christmas and are planning a small family only celebration, but that at least she has plenty of time to make alternative arrangements.
That’s it, no explanations, say it and then walk away.

All of them?

I agree with above.?

If you want her to come next Christmas I'd go with Peasblossom's suggestion Holsey.

It never ceases to amaze me just how socially unaware some people can be, and your friend sounds as if she's one of them.

Unbelievable! Why have you never talked about this before? Why have you never asked her to bring anything? I’m sorry but this is either a windup or yet another example of a woman not wanting to talk about something which bothers her.

I would strike now whilst the iron is hot( as the saying goes)
It’s a win win situation , you can get it over & done with, & she has a whole year to make other arrangements.
Best wishes, please go & do it right now.

I'd say something on the lines suggested - and soon, maybe shortly after New Year.
You don't want to have it in the back of your mind until next autumn.

Tell her to make her own arrangements next Christmas. What an utterly selfish woman don't be worrying about confrontation you don't need excuses.
Simply say you are not having any guests for dinner in future and neither are your daughters.

How on earth have you managed not to say anything for 30 years? I think I'd like to know, I wouldn't have been able to bite my tongue! what a cheeky mare

Where are all the nibbles from M&S? in you imaginary, invisible, reusable coir bag - cheeky mare friend!

I’d leave it till the Autumn and then say something like “I’m too old to do it all, so everyone’s doing a bit this year. DS (or whoever) s bringing the nibbles, I’ll do the turkey and you’re signed up for the puddings, wine and crackers.”

And then move on to the next topic of conversation.

I had my sisters in-laws for twenty odd years and they never brought anything either. ?

No wonder she's well off !!

Why are you worried about confrontation? She's obviously not giving you or your family a thought. What a nerve she's got. She's taking the p* to be honest.

It isn't clear how well you all know and what her connection is with your AC.
I'd take the bull by the horns too, but prob wait till Aug/Sept, which gives her plenty of time to make new plans. Engineer the subject coming up, perhaps early ads for hotel breaks, and then say btw you'll be making Christmas very small this year, just you and the AC. Goodness you've been patient for a long time.

May I ask what bothers you more - her self invite, her complaining about the bits, her small gift despite her wealth, etc?
What do your AC know about hosting her year after year?

How good of a friend is she? How often do you see her the rest of the year?

It has been 30 years of sharing xmas with you and your family so she must feel it is normal what she is doing.

Instead of being worried for another year, take the bull by the horns and speak up:
"Friend, for 30 years we have been doing X (whatever bothers you).
Moving forward, we will do Y (establish new boundary here)"