Understand: It’s not as if Massachusetts native Natalya Kay pined and prepared for years to be the fiddler for Gaelic Storm.The 27-year-old Kay, who grew up in Lowell and spent time in Boston before moving to Nashville, joined the popular Celtic rock group a year ago, becoming the newest member of “that band from ‘Titanic’” – the cameo appearance in the 1997 blockbuster a