I hope the OP comes back, cuz this is so hot! I read a Groundhog Day type story years and years ago, but the author got embarassed when his page got picked up by an index and he deleted it.

What if Katie follows a script like the movie, and tries to find someone to experience her last day with? She could start by killing someone she likes, maybe her favorite teacher. Then she tells the teacher what happened before, and then kills him/her again. Eventually her teacher believes her and kills her as she requests. Maybe that time she really dies, and the teacher begins experiencing Groundhog Day.