It's a film about a woman who fell in love with a suspicious hikers. Finally she realized that the hiker's sister killed his ex-wife.

Sounds like this:
http://en.wikipedia.org/wiki/Killing_Me_Softly_(film)
...Alice then goes to seek for help with Adam's sister, Deborah, only to find out that she (Deborah)was responsible for the death of his ex-lover....