Because it entirely changes the dynamic of the show? Because they had a choice between using a character who was relatively extraordinary to begin with and make her even more extraordinary, or make a random ordinary person extraordinary? They gave a (moderate) screw-up superpowers, and this is supposed to be a bad thing? Not that she's all that screwed up anyway. While bartending isn't exactly a great job, it puts food on the table for her and her sister. As a dropout, she could have done a hell of a lot worse, and we don't have the faintest idea what her long-term plans are/were. Presumably she doesn't plan to tend bar for the rest of her life, but it gives her a steady income while she's got a minor to look after. (Also, athletes are boring. *is lazy and biased*)

In spite of the insane amount of exposition that they tried to cram in there, we really don't know a damn thing about her yet. It's a little early to be making assumptions.

*is sick to death of female characters being given way more crap than male characters*