I watched a movie several years ago on TV. It was about a girl photographer who's brother worked as a horse trainer on a ranch and was murdered. The sister goes to the ranch undercover to find her brothers killer, wanting to make a calendar for the ranch. She suspects it is the one brother who she ends up falling in love with. But it is the other brothers wife, because the father left his inheritance to which ever son gets married and has a son of two years old, so she sleeps with the trainer and gets pregnant. The sister finds this out because of the birth mark on the baby is the same one that her brother and her share. The sister and the girl who kills her brother are in a sauna together and the killer sees her birth mark and knows that she was the trainers sister.
Another thing I remember was that the sister undercover rents a cottage and the sheriff goes after her too because he was also sleeping with the killer.

Hope this helps I really want to know what it is called I would love to see it again.

So any suggestions will be appreciated.

Treacherous Beauties (http://www.imdb.com/title/tt0111481/)