G.♣.
Your daughter is an adult and needs to make her own decisions regarding her faith life (or decision not to have a faith life) and regarding her use of social media. It sounds like she's making some unwise choices, but sometimes people need to learn things the hard way.
I think some people view that as a sign of strength and maturity ... that they are courageous enough to state their beliefs. That's unfortunate because people are usually more impressed by others who are able to balance being confident in their beliefs while also respecting those who disagree.
I have to say, I don't think this has anything to do with Christmas. I am a practicing Catholic. I do understand the meaning of Christmas on multiple levels, and it is an important part of my faith life. But I also have friends who celebrate Christmas as more of a fun time of year to give presents to family and friends. I would never not wish them a Merry Christmas or not send them a card or gift just because they may not share my religious views on the holiday.
It sounds like this is so much more about your relationship with your daughter. I don't have adult children, but my thought is, give her a present because you are her mother, you love her and you genuinely are wishing her a happy and peaceful holiday and a fabulous new year.
If you want to help her out financially, that's fine. If you feel she doens't appreciate it or isn't being responsible, that's ok, too. She's an adult, and it's probably time for her to stand on her own two feet. Then again, many of us need a little help from time to time, and it's not always cut and dry whether you'd be helping her or encouraging irresponsible behavior.
But don't not give her a present just because you don't see eye to eye on religion. This is a Christian holiday, but Christianity is all about loving and accepting each other, even when we disagree. Don't point out her hypocrisy. Model a life of non-judgement.