Hi! There used to be a very good Paul Simon fansite called The Dreamer of Music that had a few photos of Peggy, but it was taken down last year, in part because of a request from Harper Simon that the webmasters remove all information about him and his mother from the site.
However, here's a nice gifset from the Songs of America TV special where you can see Peggy walking with Artie and Paul.
Thanks for your question!
Paul Simon on The Game | 365
Paul Simon and his band performing “One Trick Pony”, 1980.
Paul Simon live at Queens College, NY, 1964 —
Can’t Help But Wonder Where I’m Bound (Tom Paxton cover)