I too would have liked to see her return for the Grand Festival, but unfortunately that was never going to happen, thanks to the 'Ping Pong OR Contests' choice which was laid out before her.. and the fact she was going all the way back to Kanto to play the stupid game.
Quite possibly the stupidest release in the entire series. At least the releases for the other pokemon were reasonable and you understand why it happened.
Ping pong is borderline retarded and came out of nowhere, and its not even in the games. WTF.