Donna, played by Lara Flynn Boyle in the series and by Moira Kelly in the prequel, was the best friend of Laura Palmer, and after her death she was obsessed with finding out who killed her and why, with the help of James Hurley, Laura's secret boyfriend and Donna's new love interest, and Madeleine Ferguson, the look-a-like cousin of Laura.

At the end of season two, it is strongly suggested that Doc Hayward might not be Donna's biological father after all, and that she is in fact the daughter of Benjamin Horne and half-sister to Audrey Horne. However, due to the series' cancellation, this theory has not been elaborated upon. In the final episode, Doc Hayward attacks Benjamin and although it seems that Ben has been seriously injured, Doc Hayward shows up at the end of the episode relatively back to his normal temperament.