Mystery book with horses and heiress

I'm searching for a mystery series from the 80s. A young woman named Korri inherites a horse farm. In the first book, I believe she is suspected of murdering the man she inherited the horse farm from. A detective, whose name I think is Peter, is sent to investigate. They solve the mystery and fall in love. By the second book they are married. She's 18 or 19, he's at least ten years older.

In one of the books, they find a body behind a wall in the study, in another there's a fire that burns down part of the house. Sound familiar to anyone?