Temple of Ranma's Sailor Senshi Seifuku

There was one story called "Almost Cinderella", IIRC, that has the Tendo's orphaned cousin Ranko becoming Ranma's fiancee when he shows up to the dojo.

It's been forever since I've read it, but I can think of one fic that might be what you're looking for...

"The More Things Change"

http://www.thekeep.org/~rpm/ranma/tmtc/