Is Katy Perry's music considered pop-rock or just pop?

I started chuckling the other day when I read on last.fm that says she's pop-rock. Maybe a couple of her older songs could have been considered rock, but overall, I always thought of her as another pop star because the majority of her songs don't even contain a guitar. I thought pop-rock would have been artists along the lines of Avril Lavigne or P!nk. Do I got it right or am I confused?