When the Spinosaur is reaching in the cage which is underwater, he grabs Mrs. Kirby. You can see it's claws go into her stomach, and a lot of blood comes out. Then, when they are talking about the fishing trip, Mrs. Kirby has no blood stain at all. Sure she was in the water, but still, that blood cloud was very big, and I think would stain her shirt, even a little. And besides, she probably wouldn't be able to walk all that well afterwards.