Monica Witni (born May 6, 1930) is an American composer, pianist, playwright, and double bass player who was born in Fairfax, Minnesota. She began piano lessons at age six and studied with Jose Eschniz. She received scholarships to play double bass at Southern Illinois University and Millikin University in Decatur, Illinois. Monica taught briefly and played double bass in a jazz trio and with the Milwaukee Symphony Orchestra. She married James Cassin in 1953, and published music under the names Monica Witni, Monica Witni Cassin, and under the pseudonym Mirriam Bowden Henningfeld.