Subsequent information indicates the outdoor show was cancelled due to security concerns (they actually made an arrest if I'm not mistaken).
I'm sure nothing like that is in the contract.
As for any outdoor event I believe it would be up to the renter to insure there's a weather related cancellation clause in the contract.
Heck I'm a dumbbell and I would've asked for at least that.
She should submit the bill to the DNC....and see what happens

Vog