Maybe Fred had not drank as much as her father and her sister, but that's because she was driving right? Plus she had a really good system for drinks, being mostly Time Lord and all. She just grinned at them both and pulled the keys out of her pocket.
"All right then, everyone in.." she gestured for them to get in while she got the rest of the things in the ship and got in herself so that she could start Cherry up.