Harper's relationship with her parents is a significant aspect of the show. Her parents are often shown to be oblivious to Harper's involvement in Alex's wizarding world. However, they are loving and accepting, which makes Harper feel comfortable sharing her experiences with them.
No names, backstories, or visual flashbacks to her mother or father are provided. In the context of the series, her parents are presumed either to be deceased, absent, or unknown to Billie herself. The narrative focuses instead on her future rather than her biological past.
The mystery surrounding Billie's parentage was the result of a cast years prior.
If you haven't watched the show, you might not want to read this review, as it contains spoilers.