Not to rain on your parade, but I think Gamestop is supposed to be a pretty ty workplace. They seem to have pretty high turnover on people working there too. But maybe you'll work at a good one or I could just be plain wrong. Hopefully so.

Being female, knowing something about videogames, and alreadying having retail experience will almost certainly be enough to get you the job. Can't imagine you'd need to wear anything dressier than what you described, either.