“Peter Zinovieff had his first official contact with the BBC Radiophonic Workshop on October 28, 1964, when he was given a tour of the Workshop's facilities in his capacity as a Canadian Broadcasting Corporation employee.”
On 15th January 1968, she can be seen helping him set off his Partita for Unattended Computer as part of a concert of electronic music including her own piece Pot Pourri at the Royal Festival Hall.
Shortly before Delia died, she wrote the following (of Sonic Boom):
One of our first points of contact - the visionary work of Peter Zinovieff - has touched us both, and has been an inspiration.
though in 2010, Peter Zinovieff referred to her as his 'assistant'
Interviewer: Do we hear that right? Delia Derbyshire was your assistant at some stage?
Zinovieff: Yes. She -er - I formed a
Interviewer: Lucky you!
Zinovieff: Oh! I formed a group called Unit Delta Plus and I got Delia Derbyshire and Brian Hodgson from the BBC to join me. Um. The idea was that we would make a fortune doing commercial sounds and I wasn't interested in doing commercial sounds. We did one commercial sound called Philips which was something like “wup!” and that was it. We got a lot of money for that but I didn't want to do that so we split after a bit and they went on. But they didn't succeed either. 
and I am told that in private, he says:
She was only interested in money.