Miss Amelia's List — Mercedes Lackey

The seventeenth novel in the magical alternate history Elemental Masters series follows Amelia Stonehold and Serena Meleva as they navigate property acquisition, marriage proposals, and other ancient horrors in Regency England, but with the help of elemental magic

The year is 1815, and an American, Miss Amelia Stonehold, has arrived in the Devon town of Axminster, accompanied by her "cousin" Serena Meleva. She's brought with her a list to tick off: find a property, investigate the neighbors, bargain for and purchase the property, staff the property and...possibly...find a husband. But Amelia soon finds herself contending with some decidedly off-list trouble, including the Honorable Captain Harold Roughtower, whose eyes are fixed on her fortune. Little does Amelia know that his plans for her wealth extend far beyond refurbishing his own crumbing estate -- they include the hidden Roman temple of Glykon, where something very old, very angry, and very dangerous still lurks. 

But Roughtower isn't prepared to reckon with the fact that neither Amelia nor Serena are pushovers. And he certainly isn't ready for the revelation that he has an Earth Master and a Fire Mage on his hands -- or that one of them is a shapeshifter.