While Kermit the Frog is well-known for his many appearances on Sesame Street, Miss Piggy (and her Muppet Show co-stars Fozzie Bear, Gonzo, Bunsen & Beaker, Animal, and others) have not appeared on the long-running PBS children's television series.
Although Miss Piggy never appeared on Sesame Street, she has shared the screen with some of the Sesame Street Muppets - including in episode 318 of The Muppet Show, A Muppet Family Christmas, I Love Liberty, Night of 100 Stars, Free to Be... a Family, The Muppets Celebrate Jim Henson, and other Henson productions.
Sesame Street paid tribute to Miss Piggy with a framed photo of the character displayed on the wall in a sketch about dental hygiene and in an old west sketch. In a Sesame Street News Flash featuring Old MacDonald, Kermit is caught speaking to a pig before he knows that he's on the air saying "Hey, you know you remind me of somebody. I just can't figure out who..."
Kermit the Frog is the only Muppet Show character to make any substantial appearance on Sesame Street. Rowlf the Dog made a brief cameo appearance in Jim Henson's "Nine Song" and several unnamed monsters and other characters from early Muppet productions, including Beautiful Day Monster, appeared during the first season of Sesame Street.
One possible source for the confusion may be attributed to local broadcasters curating inaccurate content alongside Sesame Street programming. For example, in 1991, PBS affiliate WLJT TV-11 in Lexington Tennessee aired a promotional spot for their "Best Friends Club" immediately following the conclusion of Episode 2882. The promo featured a woman addressing a small audience of children who sat in front of a puppet stage occupied by the unofficial use of a 1979 Fisher-Price puppet toy of Miss Piggy. "Piggy" explained the benefits of making a contribution to the station which included Sesame Street-related rewards.