The Straight Flush Hand-Stupid Bet

Robert Duvall flops a flush and Jean Smart's character flops a King high flush draw. Once we get to the river and there are 5 clubs on the board we know that a flush will win this hand. Duvall checks. Here is the dumb bet: Jean Smart is holding a King high flush, if she would have read the board, she would see that either Duval could fill a straight flush or he's holding the Ace of clubs. Either way she would lose. WHY push all-in??? Just check it down and see who wins an already large pot. No reason to shove at that moment.