I'm trying to recall a fic where in the infamous scene after being defeated on the challenge log, she goes to give the Kiss of Death, when Ranma-chan turns her head and winds up doing a kiss on the lips, signifying the Kiss of Marriage instead. Shampoo is somewhat horrified to realize what she had just publicly done (kissing another girl like THAT), but in an Amazon Village such things are not unheard of and accepted, so now she's stuck being married to another girl.
I believe she was very relieved when she later found out that Ranma was a cursed male instead of a woman. I can't recall much else about the fic, except I think they wound up staying in the village a bit longer instead of fleeing in terror, but as soon as Genma found out what that kiss meant (marriage), he grabbed Ranma and ran for the Tendos.