Maybe thank her for her concern, while smiling.. (Often, even the most obnoxious people are truly concerned about a relative's welfare.)

Then tell you're all set.

Turn away and move on. (Make sure your body language matches your words Key in communication.)

You have a trained, scientific, rational mind. It might be difficult to cope with the ongoing, seemingly irrational, rhetoric. Discussing, making arguments , is very likely to simply exacerbate her need for debate, prolonging the exchange(s) and amplifying your pain and frustration.

With brief and clear communication, you can be kind and sincere, without welcoming the rhetoric of others' viewpoints and/or discussions of differences in beliefs.

Best wishes in gracefully handling a family's typical expression of differences in varied beliefs..
A great topic to consider just before the holiday season!
Please protect yourself from uneccessary stress.