Not one word of "my sister has apologized and tried to make amends, and I know he's pressuring her to do more" (which it would still be LW's privilege not to find enough). Just "he invites her over when he knows I'll be there."

If "all" this dad wants is for his girls to be best friends--okay, one, take that off the table, not going to happen. But if all he wants is for them to be civil to each other, why isn't he putting the pressure on the one who has been abusive to reform her ways?

We all know why. It's so much easier to pressure the "good, easy" kid into continuing to make things easy for others.