The late British music producer and manager, who also worked with Jimi Hendrix, asked young Heather, who became Daltrey's second wife in 1971, if she thought her future husband's band would make a good signing for his Track Records, and she was stunned by the idea and asked him, "What are you thinking?"
She recalls the moment she first saw photos of The Who in James D. Cooper's new documentary Lambert & Stamp, and the director admits it's one of the funniest moments in the movie.
He says, "Heather was somebody that Chris Stamp ran the idea by of what was to become The Who. She was certainly around, her and her friends. She was part of the extended Track Records family - people who supported Chris and Kit (Lambert) and helped them around the office.
"She had a remarkable response in the film! I was like, 'Oh my God, what are you thinking?' Roger didn't hear that. He was in the other room at the time."
Even Stamp had second thoughts about signing the band - in the film he states, "They weren't handsome, they weren't nice. They were misfits."
Cooper admits he's not sure if Daltrey and bandmate Pete Townshend have seen his film yet, adding, "When we invited them to Sundance (film festival) they weren't able to make it. It's been made available for them to see it so I need to catch up with them and see if they have any thoughts. Basically we had 10 years of their participation, trust and co-operation throughout."
The documentary about the two influential music moguls hits cinemas in America on Friday (03Apr15).