She lets herself be touched by the aroused grandfather.
He cares deeply about his granddaughter's happiness. And when she's sad, he's always ready to improve her mood by any means necessary. The truth is, she's always been a very spoiled girl. So, if she's feeling down, she's never hesitated to talk to her grandfather and try to cheer him up. Although they've never tried making love, she's never really considered it, but now that Grandpa is touching her and she can't control herself, she's starting to understand that maybe a good fuck isn't necessarily a bad thing. The guy is too old for her, but he's her grandfather, and she knows there's no one better than him to get her on all fours and treat her right.