There was another Emma Peel before Diana Rigg. I didn’t know that until I researched Brainscan’s latest collages of Rigg as Mrs. Peel.
From this page:
After several months of auditions, actress Elizabeth Shepherd (pictured right) secured the role of Emma Peel. It was decided that a new character would accompany Steed on his missions, as Cathy Gale was so synonymous with Honor Blackman. Emma Peel was born out of “man appeal” or “m-appeal”, and thus a new era of The Avengers began.
Filming started, and Shepherd completed the episode The Town of No Return and only half of The Murder Market after which her contract was terminated. The producers felt she was not right for the part, but a definitive reason for her departure has never truly been uncovered.
Shepherd herself said: “After I was the first Emma Peel in The Avengers series, they said, ‘We welcome your ideas.’ I emanated them with ideas, but they decided I was too difficult so they got rid of me, but kept the ideas.”
This is what she looked like as Emma Peel:
Way back in 2008, Oz reported her one and only topless scene (to my knowledge) in an obscure 1970 film called Hell Boats (clicking on the pic leads to the full collage):
More of Shepherd in that role, thanks to Oz:
It would be interesting to see footage with her, although it has apparently all been lost. One of the other reasons given for her dismissal is that she and Patrick Macnee didn’t have any on-screen chemistry. Watching the footage would let us judge that for ourselves, and then give appropriate weight as to whether it was her (and her boyfriend/husband’s) suggestions that got her fired.