529 owned by a grandparent..does the beneficiary child have any "rights" to the money?

I would say asked and perhaps partly answered. Refusing to disclose anything to the OP or the presumed beneficiary may only mean that neither is a designated contingent owner, either by original account owner choice or by plan policy. It doesn’t mean that the original owner’s spouse has legally assumed ownership. There’s a chance that the 529 administrator hasn’t even been notified that the original account owner has died.