First you ask where Becca is then in the same paragraph you say Becca is in the hall.How in the world do you find Becca? I went to the movies, I went to Becca's house like it said here to talk to Sara, no Sara. I go to the stables and nothing. There is no one anywhere. I go to the school, no Sara, but there is Becca in the hall but nothing happens.
If you want help, you need to provide more information, where are you in the story, what quests are active, what events have you recently completed.
My guess is if Sara isn't at school then she is probably waiting for her fix, you need to meet her at her house in the evening, I've no idea what Becca quest you might be looking for, it might be waiting for you to resolve Sara's quest first