Who is Tina from Back When We Were Grownups: A Novel and what is their importance?

Joe Davitch's former wife, Tina, is the mother of Patch, Biddy and NoNo. Tina abandoned her children when they were quite young, leaving for England to pursue a singing career. She returned to America for NoNo's wedding, showering her daughters with affection, gifts, and unwanted opinions.... opinions that alienated the girls who were initially so happy to see her. Soon after, she disappeared as rapidly as she came.