It depends on how much she looks forward to this. Talk to her. She may be just as happy not to schlep the kids over for the day. Or she may really be looking forward to it.

Assuming you love her and still want a relationship, offer alternatives and see what she thinks. If it's that important to her, she should be willing to give something up to work a solution.

Ask her if she would be willing to host. Tell her that it has to be a politics free time and if your BIL brings it up, politely change the topic the first time, if he persists, then say "This is a politics free zone!"

Or see if you could get together the day after Christmas or another day. If she really feels hurt about not seeing you for Christmas, though, as long as she resects your rules, it's just one day a year. You can turn Christmas Eve into the special time with just your family.