In the first exterior shot of the trailer, a blonde woman in a blue-topped, pink-bottomed bikini walks by. When Gwen leaves the trailer, she passes this same woman, who is walking the same direction as before.
When Gwen/Mattie is arguing with herself in the mirror, she points at herself with her left hand. Not only is she pointing with her right hand in the reflection, but her hair is different.
A number of the same extras who pass by when Gwen leaves the trailer are later seen on the beach when Mitch makes the rescue.