I don't think she and Pearl had fused before then. Pearl seemed pretty surprised by seeing Ruby and Sapphire fuse and when they run into Garnet again, Pearl just calls her "The Fusion." If they had fused before that point she probably wouldn't have regarded Garnet as being so alien.

I think with Rose, she's only being depicted the way she is ("older wiser lesbian", as OP put it) because we're mostly seeing her through the eyes of other characters/other characters' stories. The one time we saw a completely objective view of her, in Lion the Movie: Straight to Video, it was after she met Greg and learned more about humanity. I agree that with the limited screentime Rose has had, it's...not really a huge deal. We still have a lot of story to go through and learn more about her.