she doesn't want to be Shamita true but somewhere she wants to be like Shamita. Teja and Karan have known each other from before. She knows about his ex's too but may bot be in so detail but she was saying she once met him with his ex to Jay .
I don't think she wants to be shamitha as Teja actually thinks very high of herself. She just jealous that Karan always patches up with her every time. I don't see anything beyond that. I didn't know Teja and Karan are friends from before as Teja doesn't seem to know about karans past yet.