I worked on a hip and knee replacement unit for years and I'm seriously shocked they agreed to operate on her. My trust had really strick rules about BMI, I think the max was 33 or 35. I've watched many hip replacements and that surgery is BRUTAL the surgeon has to basically dislocate the leg, pull it out of its socket, then they put the leg in an unnatural and twisted way on their shoulders so they can access the hip joint. Poppy's surgeon will have to be the strongest man in Britain to be able to hold Pops floppy leg over his shoulder. Not to mention recovery time and the immense pressure of her weight on the synthetic joint.
A lot of people faint the first time they stand up after the operation due to the anaesthetics and the OTs normally 'catch' them and guide them down to the chair. No way anyone can catch the SuperEater.