I think she actually sounds better and writes more coherently than most of the metal the guys here listen to.
Not at all. You can't even compare metal and pop side by side, first off because they're completely different genres both in sound and purpose. Second, they actually play their instruments and write their music, putting honest hard work and meaning into the lyrics. Yes, some sound similar, but each band has their own twist and interesting addition to the metal scene, not to mention there are at least a dozen different types of metal.
Pop? The only real singing, if you can call it that, is the lead vocalist who is only supported by a machine. Even the singers voice, in pop, is typically auto-tuned even slightly.
I could go on, but I don't think I need to. You can't even compare the genres is my main point, so don't even bring the structure of the songs into this because regardless of the genre, most song structures are the same.