I Quite Enjoyed The Movie (SPOILER)

I happened to get it as a free rental and thought it was decent, although that lead actress who played Heather irritated the ish out of me! The wishy washy attitude with her father (and I enjoyed seeing V. Jones in a leading role, which I'm not used to seeing), as well as her wishy washy ways with the guys who were interested in her too got on my nerves. SPOILER COMING...now that I understand that she was the one behind most of the super natural things happening, I can understand, somewhat, the conflicted ways she was portraying, but I'm trying to figure out her intentions. Why did she kill the guy that liked her instead of just leaving him alone completely? Or even the preacher for that matter? And are we to understand that Robbie had no powers whatsoever in any of the instances?

SC