Tell her straight out that you are entitled to your opinion, and she to hers.
This being so, she must respect your right to say that no-one who has not been fully vaccinated witll be allowed into your house at any time.
I realise it is unpleasant, but if you give in over Christmas you will worry if she sneezes or coughs and once you have had her to stay at Christmas you can't very well turn her away at any other time she wants to come.
If she did come, what would you do or say if someone who is vaccinated came by? Let them in without telling them that your other guest is not vaccinated, or feel forced to say, as I would feel, "You're welcome, but Annie here isn't vaccinated" ?
Right now in Denmark we have an increase in cases of covid19, mainly amongst the unvaccinated, but they can spread the infection to people who have been vaccinated.
By all accounts, covid 19 is not a minor or pleasant ailment, even if you are vaccinated against it before contracting it.
So stick to your guns.