The first half of season three is them travelling to the tree of life. They'll probably meet Rani when they get there. They have to be pretty close since the desert was one of the last landmark's on Rafiki's wall.
I hope so, that means we will have several episodes left after the "mama Binti" episode... do you know how mich episodes have to be revealed yet? I hope Rani is in all of the not revealed yet episodes