I can't help but think that whenever Mabel is in between reincarnations, she "haunts" him to lighten the mood for her not being alive anymore. Like if something makes dipper uncomfortable, he can just hear Mabel laughing triumphantly somewhere, as he sorts of freaks out. Or if he meditates, she would drop by to put an uncomfortable thought in his head, " BOOOOO! you are now thinking about twin souls, Enjoy that thought! OOOHHHHH"
Oh she doesn’t just haunt him, she full out visits him!
That being said, she definitely does pull some ghostnanigans on Dipper too, just to fuck with him. Gotta keep this boy on his toes somehow!