Margaret is Ethan's grandma and Nadia's step-grandma. She's also the former principal of Epiphany Middle School, and an old friend of Mrs. Olinski's. In fact, she gave Mrs. Olinski a lot of important support right after the car crash, which happened ten years before The View from Saturday begins.
Margaret does a lot of good things for a lot of people—and animals. She's worked hard to become legally certified in saving turtle hatchlings down in Florida. She helps Nadia's mother to get a new start in Epiphany. She supports The Souls by coming to New York to see them compete. And she's found love again, with Izzy, long after being widowed.
Loving, kind, and utterly self-confident: Gee, she sounds a lot like a Soul, doesn't she?
But she doesn't seem that warm or loving to Nadia. Instead, Nadia sees Margaret's goodness as "interfering," especially in the beginning:
It was obvious that it was Margaret who had made possible my mother's leaving my father. Margaret Diamondstein, formerly Draper, helped my mother move to New York. She moved turtles from one nest to another. She moved Grandpa Izzy out of Century Village. And now, she was helping my father get permitted. By next turtle season, she will be helping him move to the beach. Margaret Diamondstein, formerly Draper, was an interfering person. ("Nadia".150)
You know what? She totally is interfering. What Nadia doesn't realize (yet) is that sometimes interfering is an act of kindness.