The daughter of English actor and radio presenter Neil Landor and of an Irish mother, Rosalyn was educated at the Royal Ballet School, Richmond, and at Tolworth Girls' School, in Surrey.
A child actress in British films in the late 1960s and early 1970s, her career took off in the 1980s in English television work - notably in Love in a Cold Climate (as Lady Polly Hampton), Rumpole of the Bailey (Fiona Allways, a lawyer), and CATS Eyes. The last of these was a UK television series akin to Charlie's Angels, in which she played the leading role of Pru Standfast, head of the 'Covert Activities - Thames Section' of the British government's Home Office.
Rosalyn also appeared in stage plays, including a 1983 revival of Noel Coward's Hay Fever.
Well known in England, she moved to the west coast of the US in the second half of the 1980s and married an American architect. Rosalyn now has two daughters, Arielle and Sophia and lives in California. She continues with her career, including voice work for Disney and Books on Tape for Random House.