You don't say whether you need teen or adult fiction. These are adult books, but they are fine to read as a teen.
The Gaslight series by Victoria Thompson is a mystery series set at the turn of the last century in New York City. Sarah Brandt is a recently widowed midwife, born into a wealthy family but who works in the poorer parts of the city, mostly. She solves the mysteries along with an Irish policeman, and they struggle with the fact that they're falling in love even though they're in different social classes. The first book ia Murder on Astor Place. http://search.barnesandnoble.com/booksearch/results.asp?WRD=murder+on+astor+place
Thomas/e/9780743256193