Who is Brandy McCabe from The Mirror and what is their importance?

Brandy McCabe is Shay Garrett's grandmother, transported by the mirror into Shay's body in the future. She gets the surprise of her life when she discovers she is in her granddaughter's body and has watched her granddaughter die in her former body. Brandy plans to runs away the night before her marriage to Corbin Strock, who she does not love and is afraid of. She longs to go to the university and learn, but before she can set off for Aunt Harriet's house she is switched by the mirror. Though she tries to pretend to be Shay, she has no idea how to behave in Shay's world. Everyone can tell she is different, including her fiance Marek Weir, to whom she is uncommonly attracted. When the family discovers that Shay is pregnant, Brandy overhears them talking about abortion and runs away. Shay briefly re-inhabits her own body and takes them safely to Mr. St. John's house, where he nurses Brandy back to health. Brandy is more comfortable on Mr. St. John's farm, where she does not have to pretend to be anyone else and he believes her story. She is uncomfortable with her reaction to Lottie's photographs. Although she is a progressive woman for her own time, she is hopelessly old-fashioned in this world.