Enchanted Time by Amy Elizabeth Saunders
I enjoyed this story.
The description of the book I am listing below is from the back jacket of the book. I'm adding it because I believe the one on the Goodreads page does not depict this story.
With an antique store to run, Ivy Raymond had an eye for members of the opposite sex, as long as they were named Shakespeare, Rembrandt, or Louis XVI. But she was too busy to look at men from her own century. Then a kooky old lady sold her a book of spells, and before Ivy could say abracadabra, she was living in a crumbling castle with a far-from-decayed knight.
Stripped of his land, wealth, and title, Julian Ramsden was still arrogant enough to lord it over Ivy. But the saucy wench had powers over him that he could not deny. Whether the flame-haired stranger was a thief, a spy, or a witch, Julian was ready to steal a love that was unquestionably magic.