For more than a half century, nearly every prominent singer to perform at the Metropolitan Opera could expect to be approached backstage afterward by a wispy woman wearing thick eyeglasses, who held piles of memorabilia to be autographed while she praised the performance in a raspy Brooklyn accent.

This was Lois Kirschenbaum, one of New York’s biggest and longest-standing opera buffs and a nightly staple at the opera since the late 1950s.

Few operatic performances took place at the Met without being observed by Ms. Kirschenbaum, usually from a seat in the uppermost balcony. And few prominent singers went home without signing numerous items for Ms. Kirschenbaum, who had befriended some of the world’s most famous opera singers, from Beverly Sills to Plácido Domingo.

Ms. Kirschenbaum died March 27 at a hospital in Manhattan. She was 88.