Pop'n is pretty casual, so she might actually enjoy it. They've been pretty good about keeping a steady flow of licensed anime music as well.
And yeah, controllers are a bit on the pricey side. Gamo2 has them for $234, but the shipping (from China, via EMS) is pretty crazy.
However, there is a Round 1 arcade at the Stone Crest Mall in Lithonia, and according to ZiV they do have a Pop'n machine (as well as the latest IIDX, DDR, Pump, Gitadora, etc). Wouldn't hurt to give it a shot.
If she doesn't like it, there's plenty of other stuff to do there, too.