disa o'brien, portrayed by jan graveson, first appears in episode 536. she is introduced as a tough seeming wearside runaway, who helps diane butcher (sophie lawrence) to survive when she lives rough on the streets. disa first appeared in flashback sequences involving diane on 27 and 29 march 1990, before returning from 18 december. the character was written out of the series the following year and departs in episode 633, first broadcast on 28 february 1991.