In the movie, Sally is married to Gabe, who is abusive towards Percy. He is portrayed as a lazy, overweight, and generally unpleasant character who constantly belittles and mocks Percy. He does not believe Percy's stories about monsters and the divine world.
In the movie, Percy eventually leaves home and runs away from the abuse. He is not reunited with Sally in the first movie, but it is implied that they eventually reconnect in the later films.
It is important to note that this family dynamic does not exist in the original books. The books portray Sally as a loving and supportive mother who is separated from Percy's father, Poseidon. She is not married to Gabe Ugliano, and Percy's only "stepfather" in the books is Luke Castellan.
The movie took some creative liberties with the source material, including the introduction of Gabe Ugliano and the overall dynamic of Percy's family life.