Stefan insantly took to Ember because she was the Doppelganger of Caroline - and his friendship with Caroline was something he treasured. Ember developed a crush on Stefan after meeting him. She loved how kind he was and how he behaved around everyone. Stefan invivted her to stay in the boarding house and she couldn't have been more than thrilled. When Stefan turned into the Ripper, her feelings didn't change for him and she still tried to keep around him as much as possible and help him get back to himself becoming like a new lexi for the Ripper.