I will categorically state that Jesus would NOT be “overjoyed” that a child would be raised in such as situation, nor would He sit and chat with them without commenting on their blatant sin. We have example after example of Jesus doing just that in the New Testament.
YOU knowing what Jesus would do and feeling the hostility you do towards your family member, I only feel sadness for you...........May Jesus turn your heart from condemnation to acceptance.
The obvious solution to your problem is to forbid your family member from ever stepping into your house again, citing your religious belief of course, and condemning her and her partner and their unborn child to eternal hell in front of the entire family.
That should work for you..........
Let me know how that turns out, I’m sure your Christmas will be everything it’s supposed to be once purged of that sinner...........