Just visit Savi after sparing and the first sex event.
Also, I will make some changes in this event so even if you still can't trigger it just wait for the next ver. It should be easier then ^^
And she is Savi's mother, not sister :)
Welp, I had to start over from scratch on a new save file but I finally unlocked the boar girl's mom. Fu*k!
(And I expressed that not in the fun way)