How can you compare Idgie and Evelyn's friendship in "Fried Green Tomatoes"? What can they both relate to?

Do you mean Idgie and Ruth, or Evelyn and Mrs. Threadgood?  Idgie and Evelyn didn't have a friendship.  Evelyn was friend with Mrs. Threadgood. " Virginia Cleo Threadgoode, Ninny, is the one who tells Evelyn about Whistle Stop. She grew up in the town and married Idgie's brother, Cleo. Her stories and yarns are "threaded good" but seldom involve herself, as she has spent most of her life as a spectator. She is a wise old woman who teaches Evelyn what she needs to know to become a full adult and be happier with herself."  She met her when she went to the retirement home with her husband to visit his aunt.  Evelyn struck a friendship with Mrs. Threadgood because they were both lonely.  Evelyn was not close to her husband because he was all about work and baseball.  He didn't really pay much attention to her.  Mrs Threadgood was lonely because she was in a retirement home with no family and as far as we know, no friends.