Complex sentence: The role was played by Patricia Roe from July 1968 until March 1972, and by Alice Hirson from March 1972 until the character's last appearance in May 1976.
Split into simpler sentences: The role was originated by actress Patricia Roe from July 1968 until March 1972, when Alice Hirson assumed the role. Hirson played Eileen from March 1972 until the character's onscreen exit in May 1976.