“A soprano who joined the Met in 1966 as a member of its adult chorus, Ms. Doria took the helm of the children’s group in 1986. For the next 23 years, until she stepped down in 2009, she superintended her charges – who ranged in age from about 5 to the early teens – through weekly classes at the opera house, through stage rehearsals and, like an operatic Momma Rose, from the wings at every performance.”