Yes, REINSURE is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, I 1, N 1, S 1, U 1, R 1, E 1.

Is it a valid word?

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

provide additional insurance for
insure again by transferring to another insurance company all or a part of a liability assumed
insure again by assuming all or a part of the liability of an insurance company already covering a risk