Ellen Albertini Dow

Ellen Rose Albertini Dow (November 16, 1913 – May 4, 2015) was an American film and television character actress and drama coach. She portrayed feisty old ladies and may be best known as the rapping grandmother Rosie in The Wedding Singer (1998), performing "Rappers Delight". Dow's other film roles include elderly lady Mary Cleary who "outs" her grandson in Wedding Crashers, Disco Dottie in 54, the recipient of Christopher Lloyd's character's slapstick in Radioland Murders and a choir nun in Sister Act. She was best known to small screen audiences for her guest appearances on sitcom The Golden Girls. Description above from the Wikipedia article Ellen Albertini Dow,licensed under CC-BY-SA, full list of contributors on Wikipedia.
Cast

Patch Adams
Aggie

54
Disco Dottie

The Wedding Singer
Rosie

Munchies
Little Old Lady

Ready to Rumble
Mrs. MacKenzie

Wedding Crashers
Grandma Mary Cleary

Annie's Point
Louise Tette

Not Another Not Another Movie
Rose

The Blue Hour
Unknown

Radioland Murders
Organist

Road Trip
Barry's Grandma

Going to the Chapel
Grandma Haldane

Frank the Bastard
Dora

The Invited
Natalie Shaw

Eight Crazy Nights
See's Candies Box (voice)

Longshot
Ms. Fleisher

Carnival of Souls
Mrs. Meltzer

Fat Girls
Mildred

Space Case
Betsy

Sister Act
Choir Nun

Sister Act 2: Back in the Habit
Choir Nun

Problem Child 3
Lila Duvane

Memoirs of an Invisible Man
Mrs. Coulson

My Blue Heaven
Nun

Without a Paddle: Nature's Calling
Mrs. Bessler

Blood and Concrete
Old Lady