No sexual assault occurs on screen, but it's definitely a theme of the film. There is a slightly uncomfortable scene where a male character asks the female character for a kiss and then chases her through the woods, but she is never in real danger. Wolves (representative of men) killed the protag's older sister at the beginning of the film, and at the end they break through the protag's window as she screams in terror. Considering thematic implications this could be stressful to watch
The film is about female puberty and sexual awakening, which is mostly told through metaphor. The third act has Rosaleen have a wolf encounter of their own, and their interactions are sexually charged. Rosaleen is a child character, while the wolf is played by an adult man. It's meant to be a similar situation as Sarah and Jared in Labyrinth, where the antagonist is a hot dangerous man intended to represent growing adolescent sexuality, but may be more uncomfortable due to the presentation, especially since it's revealed the wolf isn't really a villain. The two kiss onscreen, as well, which could be a concerning element of the film.
The entire movie takes place in Rosaleen's dream during what's implied to be menstrual cramps. While it's shown in the opening scene that she is an 80s-era adolescent, the dream takes place in an 18th-century village. The film uses a lot of surreal, dreamlike imagery intended to represent various aspects of female puberty, sexual awakening, and passage into adulthood.
There is body horror, not body dysmorphia. No character talks about having negative, let alone unrealistically negative, perceptions of their body. Body horror and body dysmorphia are not the same thing.
Main character wakes up and looks over to her parents' bed where they are just finished having sex. She mentions the noises afterwards. You don't see anything and it's so quick I don't consider it enough to be labeled sexual content.