What happened to Teen Titans?

Answer 1

she erupted a volcano and wasn't seen for some time but know one knows why she didn't remember anything in episode things change

Well, she causes a volcanic eruption that kills slade and almost kills the titans but she takes control of the volcano, and stops the eruption, causing her to turn to stone. In a other episode, "Things Change", Beastboy finds a girl looking just like Terra, but she denies being her. Although, it really was Terra, she denied being herself because she wanted to forget the past..

Answer 2

Cartoon network decided they wanted to focus more on there own TV shows and cancelled the show before the rest of the season was aired (which had all ready been created)

Answer 3

She was turned to stone as a sacrifice to save the city. This happens in episode 26 (Aftershock pt. II).

Answer 4

She was never in Teen Titans, or at least the Teen Titans on Cartoon Network. She was, however, in the Young Justice comics.