Yes, READINESS is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, A 1, D 2, I 1, N 1, E 1, S 1, S 1.

Is it a valid word?

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

the state of having been made ready or prepared for use or action (especially military action)
prompt willingness
(psychology) being temporarily ready to respond in a particular way
a natural effortlessness