Worlds Enough...And Time
by Kristine Kathryn Rusch
Whenever things get rough, Roxanne escapes to other worlds. She has a talent that that no one else believes exists. Except her granddaughter Marissa, who exhibits the same talent. Marissa, who can open windows to other worlds. Roxanne wants to train Marissa to live with her talent, but the rest of the family wants to stop her.
With complete bonus story, "Watching the Music Dance."