Rosina and the Travel Agency by Jill Hand

After more than a century of conducting tourists to the past and back again, sixteen-year-old Rosina is tired of working for the Travel Agency, a powerful twenty-fourth-century enterprise that is in the business of time travel. Rosina compares living and working with her fellow teenage time travelers to being stuck with your high school classmates for centuries, and is beginning to wish the Agency had never recruited her from Victorian England. Then Rosina's boyfriend, the exasperating but intriguing Ned York, reveals his surprising true identity, and asks her to join him on a dangerous mission. Rosina agrees, with unforeseen results.