Demi's going to be the club pres's older sister and kind of an unofficial auntie to people who hang around the mc, although her real job is that of keeping this rowdy bunch of kinds out of prison. Sometimes she succeeds, sometimes the law wins. She went away for a bit during/after college, but she's been back in town for ten-ish years and would've likely known both Viv and Rory as they were growing up.