Cha Cha is Leo's Gal. Cha Cha smooches Kenickie at the dance. Cha Cha may have been Danny's gal. Cha Cha is everyone's gal. Which means the Pink Ladies hate her. Take this snide comment from Frenchy (please):
CHA CHA: I'm the best dancer at Saint Bernadette's.
FRENCHY: With the worst reputation.
We love Frenchy, but Cha Cha's reputation has nothing to do with her dancing. And, frankly, her reputation isn't any worse than Rizzo's. Cha Cha is too busy dancing up a storm to pay attention or care what anyone thinks of her.
Cha Cha, despite having two names, is a fairly minor character. She's a catalyst in Sandy and Danny's breakup, although we're not sure why. Sandy gets mad at Danny when she asks about Cha Cha. Is the issue that he was with Cha Cha or that he lies about it when asked? Or that Cha Cha is a better dancer? Australia may be on the other side of the world, but that's no excuse for Sandy's backward logic.