How serious is she with the games? There's a big difference in performance in durability depending on dance pad type.
Soft pads are on the low end, hard pads in the middle, and metal pads on the high end. Of course there are quality differences between pad makers as well, but that's a general rule.
www.Redoctane.com has a really nice "soft" pad that actually works really well. It's $80 though, which is on the high end for soft pads. Their metal pads are reviewed well also, but I've never used one. Cobalt Flux pads (
www.cobaltflux.com) are the Mercedes of DDR pads, and the price shows that. They are for serious players (or rich folks) IMO.
If she's just starting out, or this is her first time actually using a dance pad, go on eBay and grab a 2 pack of the soft pads so she can try em out. I used them for at least 6 months fairly regularly and they held up well. I moved on to other pads after that, but only because I knew I wanted to keep playing. Plus it was under $40 IIRC for the pair.