Oh, I don't think it's a tough lay down at all. I'm calling with worse than 2-to-1 when I'm clearly beat. Indeed, the best play is to check on the river so as not to be bluffed off the best hand, if I think she's capable of a check-raise bluff at all. I could argue that value-betting the river is right, because she calls with any flush of her own and only check-raises when she's full.