Peggy is, I would assume, the aunt* Sharon talks to on the phone when we first see her coming out with her laundry basket. As we didn't get much of Sharon's story (like not even her last name, I would have loved to see Steve's reaction to her name), I would assume that's just a nod to the people who are familiar with the comics.

*Unless it has been officially stated that she is Sharon's grandmother, then idk.