I can’t remember much more but the son of his father invite with them her best friend and she tries to have sex with her father but he don’t want it.
In one scene she appear without clothes in a beach with the father of her friend and she tries to get the father to enter the water naked with her.
Besides, this two teens have brown hair and are alike between them
Possibly Blame It On Rio (1984)
with Michael Caine and Demi Moore