Steve, her second cousin, confirmed that Mandy in no way disappeared, she merely changed her name to Miranda Forbes and continued working in small roles across numerous TV programmes in the 70s right through to the late 90s such as Coronation Street, Minder, Lovejoy, The Bill, Ab Fab and Yes Prime Minister, often playing secretaries or nurses.
On checking this on IMDB (who lost Miranda and Mandy as two separate people-I've sent this info to them to combine the credits) I saw that Mandy also appeared in an episode of Casualty in 1991 that I have in my rare collection, and I've taken a couple of screencaps of her in her role as a GP's receptionist. Here she is opposite Edna Dore
Sadly this discovery is tempered by the news that Mandy tragically and prematurely died in 2001 aged just 55.
My condolences and thanks once again to Steve and a belated RIP to the wonderful Miss Weet.