Would people consider it more fair to charge based on ideal weight rather than actual. Since I am 6ft3 and 90kg, I can hardly be blamed for having more bones than next to a girl who is 5ft and 60kg, it's just nature. However if she is 5ft and 90kg, then she should pay more??
Is this going a bit nazi'ish?
And it's nature that she needs more clothes and shoes than you but I don't see her getting a free ride in that department.
If she is 5 ft and 90 kg she can afford to save up the extra by cutting down on the amount she eats. That's real blimp territory.