The Soprano Sorceress — L.E. Modesitt Jr.

When Anna Marshall is transported from her boring and frustrating life in Ames, Iowa, to the very different world of Erde, she's angry and confused, but soon finds out that for the first time in her life she's uniquely powerful. In Iowa Anna was a music instructor and small-time opera singer, but on Erde her musical ability makes her a big-time sorceress--potentially.

First she must figure out how to use her ability before the big-time rulers who've noticed her arrival kill her just because she's an unpredictable new power. . . . Those rulers may wish they hadn't waited as long as they did.