As a hunter, the onus is always onus to determine sex, shootability etc... we cannot blame the PH in my mind. When I pull the trigger, I MUST be sure of my shot, the safe area behind the shot and what I am shooting at... I cannot shoot a Gemsbok and then claim I thought it was a kudu, for example!!
The PH was in charge of the hunt, if his client shot a female leopard then how is he or she not wrong.

I fail to see the logic. The money is another issue entirely.

But a lot of mistakes were done on this hunt.
Opposite perspectives. I'd say both are right. Here's why.
From a legal perspective, the person holding the rifle and pulling the trigger is always responsible for whatever he shoots. If the PH tells you to shoot a person, and you do, you are responsible. I don't believe the person behind the trigger would or should be able to shirk responsibility. So that's the legal perspective, and that gives us the answer as between the hunter and the landowner/Government of Zimbabwe. Trophy is forfeit, and a fine must be paid (at least this would be the case on National Parks lands).
From a practical - and maybe even moral - perspective, this is, though, the fault of the PH. Very few leopard hunters, particularly first timers, will be able to properly sex a leopard while sitting in a blind. Not only is it difficult to do unless you get exactly the right presentation in the right light for the right amount of time, but your window in the blind is likely (more rather than less) covered by a rifle on some sort of rest. (You could try to do this by looking through a scope, but you'd have to be pretty special to be sure enough that you got it right to allow you to take a shot with confidence.) Add to that the fact that your PH will want to make the determination himself, and will likely want you to sit perfectly still and not fumble around with binos when you should be getting ready for a possible shot, and you have a situation where the hunter is completely dependent on the PH for this decision.
In a perfect world, if the PH messed up, you'd get another shot at a different leopard. If that isn't possible, some sort of compensation should be offered - starting with the PH's employer paying the fine.