Sharon Priestley was the blonde-haired girlfriend of Mark Casey when he joined Casey's Garage in 1989. After putting in his first shift at the garage, Mark went along with his new boss Kevin Webster to a surprise party for Curly Watts at the Corner Shop flat and brought Sharon to show her off, although the girl was less than pleased at being dragged along to a party full of strangers. Introducing Sharon to Kevin, Sally, Martin Platt and Jenny Bradley, Mark joked that he didn't know if she fancied him or his car, to which Sharon replied that she didn't either. The party was a blow-out as Curly, who had been studying for an exam the following day, turned the guests away the moment he arrived home, much to the embarrassment of his partner Shirley Armitage who had thrown the party to celebrate their year living together.
On a later day, Sharon turned up at the garage to see Mark and remind him that she was finishing work early that day and to be there to pick her up. Mark promised to meet her, despite having to leave the garage early to make the appointment. Although angry that Mark hadn't cleared it with him, Kevin let the matter pass due to Mark being owner Tom Casey's son - an arrangement the lad was taking full advantage of.