In seasons 1 through 9, Peggy's mother has been shown many times in flashbacks (and in the present). In the flashbacks, Peggy's mother is shown as a woman who resembles Peggy only with long hair and different glasses. In the present, she looks like she did in the flashbacks only with gray hair and a different outfit.

But then at the start of season 10, an episode was shown where the Hills visited Peggy's mom at Peggy's childhood home. There, Peggy's story was changed. In this episode, Peggy spent her childhood on a ranch, but in the seasons 1 through 9 flashbacks, Peggy spent her childhood in a suburban home. Also, Peggy's mother is different. She is now shown as a thin, elderly woman with extremely short gray hair who is very critical with Peggy.

Unless Peggy has 2 mothers, this is a slip-up.