Sounds like the typical Mother-in-law
Look at it this way: if she's bothered by you not going, then that means she wants you to be there and part of the family! However, there comes a time when you just can't always please everyone, and instead need to worry about
your own health and well being. I agree with achievinggrace - your husband should be supporting you when it comes to his family gatherings and whether or not you're feeling up to going.
Do you have anything planned for the Christmas weekend, or is it all this Tuesday and Wednesday? Consider how you want to spend the holiday and whether the pros outweigh the cons of postponing your Flagyl date. Don't let the pressure get you to. That's not what the holidays should be about
.