But, she's far from her hometown. The news is reporting she's from College Station, Texas which is home to A&M University. She's 20, but she may or may not be a student. Maybe she wasn't hurt that badly and was too shaken up? The reports describe the knife-wound as a "scratch" not a laceration. Words are important. Maybe she wasn't supposed to be in Pittsburgh and didn't want to get in trouble? Maybe her mother is a doctor and she wanted to talk to her instead?
There could be lots of different reasons for this and it's probably foolish to openly speculate why she didn't want treatment.
At the very least, I think this report should be taken seriously. This isn't a weird LiveJournal story from some college girl. All these details came straight from the police who are investigating the situation. And, this happened yesterday. They've had time to mull this over.