What is the movie about the teenage girl whose father has post traumatic stress disorder?

MarkThrone: What is the movie about the teenage girl whose father has post traumatic stress disorder?
It was a movie about a teenage girl that had a father that was effected by the war and in a part of the movie he cheated on her mother with her sister. She also lived near the desert where they tested bombs, I think. There was a scene I remember when she is hosting a party at her house and the boys are standing on one side and the girls were on the other. I assume the movie was set in the sixties.

Answers and Views:

Answer by Marcus W.
Im pretty sure it was a chick flick. Was it Twilight, New Moon, or the Sister Hood of the Traveling Pants? Those are the only three I heard of/seen before.