Shinn, Sharon. Gateway.
Daiyu, Having been adopted from China as an infant, is happy with her family, job and friends in St. Louis. After going to a fair, she is attracted to a black jade ring, and goes back to buy it. When she puts it on and travels under the St. Louis Arch, she is transported to another world where most people are Chinese. She has been brought to the dimension to remove the evil prime minister, Chenglei, who is oddly charismatic. While learning how to be a lady so that she can attend a ball and dance with Chenglei, she falls in love with Kalen, a poor young worker. There's intrigue and adventure aplenty, good dollops of romance, and a satisfying ending where things work out for Daiyu back in St. Louis, even though she doesn't remember anything of her adventure.
Moved almost all of the 7th grade language arts books out of the library, made a good start on 6th grade, and will work on the 8th grade later. Slowly but surely getting ready for the big renovation that starts in (gulp) two months!