so many plotholes...

at first i thought it was a clever ending, but now i'm thinking it makes no sense. for instance, why did she just suddenly notice the shoes on the train car, when she killed the girl earlier?w ho did she kill on the roof? they seemed to be implying that the crime actually did happen. also, how was this little woman able to lift an overweight lady up, and throw her through a glass window? the whole thing makes no sense.