The trailer for this movie starts as follows: A couple were laying out getting some sun and a little R&R (think it was a lake) and nearby were a loud group of kids. The gentleman asked the kids to turn down their music and the kids just ignored him. He got up and turn it down for them which set off a chain of events. The kids harrass the couple, eventually kill the husband (or boyfriend) and the wife (or girlfriend) take revenge (Rambo style) on each of the punks responsible. Looks like it took place in lush scenery.

Eden Lake (http://www.imdb.com/title/tt1020530/)

She doesn't actually take revenge on them but it is more of a fight for survival. Excellent film but terribly brutal.

That's it! Thanks. You're right it is survival first but she sure gets back at them.