P.C. Cast - Partholon

Divine by Mistake (Partholon #1) 

by P.C. Cast

The most excitement teacher Shannon Parker expected on her summer vacation was a little shopping. But then her latest purchase--a vase with the Celtic goddess Epona on it--somehow switches her into the world of Partholon, where she's treated like a goddess. A very temperamental goddess…
It seems that Shannon has stepped into another's role as the Goddess Incarnate of Epona. And while it has some very appealing moments--what woman doesn't like a little pampering now and then?--it also comes with a ritual marriage to a centaur and the threat of war against the evil Fomorians. Oh, and everyone disliking her because they think she's her double.

Somehow Shannon needs to figure out how to get back to Oklahoma without being killed, married to a horse or losing her mind….