Forcing a family
Here we have another case of a blended family not really all getting along as well as they might like. When so much time has passed and the children involved are adults, it’s possible that the ship has sailed, and they’ll never be best of friends.
This is totally fine, and forcing it will just have worse results. This sister who feels like they should now all be bosom buddies when she’s not really put the effort in for all these years is being a little unreasonable.