Yes, MADONNA is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, D 2, O 1, N 1, N 1, A 1.

Is it a valid word?

MADONNA is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the mother of Jesus; Christians refer to her as the Virgin Mary; she is especially honored by Roman Catholics
United States pop singer and sex symbol during the 1980s (born in 1958)

Also: virgin mary, the virgin, blessed virgin, madonna louise ciccone.

Not playable in Scrabble US: MARY.