she is entitled to get on the plane and be treated with respect
Well said
There is absolutely no reason whatsoever why she couldn't be safely accommodated in a hold cage with all the other overweight baggage.
For the sanctimonious amongst you perhaps you ought to decide which passenger has the right to greater sympathy - the grossly overweight who are costing you a fuel penalty and can sometimes seriously inconvenience adjacent pax; or the pax who has also paid their dough to be conveyed in a manner which they thought they would be without some lard arse pressing them up against the cabin wall.