Yesterday I delivered a 21st cake to a girl whose mother had provided me with the brief. She had originally sent me a photo of the cake the daughter wanted that had been taken at a function under lights. I suggested to her mum that it was not the done thing to recreate someone else's cake particularly when I had no idea where it had been made and couldn't give credit to the original designer. I discussed swapping out some of the colours in order to make it a little different and explained that it wouldn't be exactly the same but I would recreate it as best I could for the budget she had given me. 

When I delivered the cake to the event, the daughter got out her phone, obviously comparing it with the photo she sent me and started picking apart the cake in front of a room full of caterers. I was so embarrassed. She then shirt paid me as said it wasn't an exact replica. I  now have to create a wedding cake this week and am struggling to put this behind me.

Aw, that sucks. If someone wants "an exact replica" of anything tell them you can't do it.  I can't even duplicate my own work sometimes much less someone else's! If you start off with no usually they'll back off the exact part and settle on "close". If they stick to the whole "exactly like ________", you can bet they'll be giving you a hard time after you deliver.

Each cake is a chance to start over. Do what you do best and let the rest go. 

What pastrybaglady said. 

I sometimes love other people's cake creations, and use for inspiration, or to work out the method they used to create something, but I tell people that If they want a replica, exact one - I can't do it. It will be different somewhat, from the picture they sent/give me. It is hard sometimes to not repeat someone else's work, when it is for example a pop-culture image (there are only so few ways one can do a Mickey Mouse shape, or a Wonder Woman color scheme for instance). But especially with wedding cakes, exact replicas are not possible, IMO... 

Did you give her a sketch of what your cake may look like, with alterations to change the design a little? I am not saying you should have. It helped me though in one similar instance, when I was given a picture, and a request "can you make this?!" - I sketched quickly and roughly, together with same words as yours - about changing it here and there, and adding-removing some elements, colors, etc. And the customer said "Oh, I like your idea even better!". And she was a pretty fussy, alpha-perfectionist kind of a woman. Perhaps, giving a rough visual of what to expect, would have helped?... I dunno, just a suggestion.

You already told her that it wouldn't be the exact same and shouldn't have let her get away with it. Stick to your guns from now on and if that was me I would have grabbed the cake and left! Ignorant people can be brought down to size too.

Also...Never deliver a cake that hasn't been pain in full ahead of time. Don't even turn your oven on if they haven't paid in advance. And if someone doesn't want to pay you the amount they owe you, take the cake and walk away with it.

What ^^^she said................and, I think you got played--the old "save a few bucks by tearing it down publicly trick". 

In your shoes, I'd have reminded her [loudly] that I told her it wouldn't be "exact" and I'd have picked up the cake and walked out with it.  Maybe, and it's a tiny maybe, she'd have gotten it back if she'd have paid me in full..........if I hadn't accidentally tripped and dropped it...............

Always get paid before delivery.

I agree with maybenot....Mom KNEW cake wouldn't be EXACTLY like the one her daughter saw, Mom KNEW daughter would throw a fit as she is an immature 21 year old brat and it was Mom who discussed all of the details with you, NOT the brat.

This is why a lesser amount of money was "ready to go" when delivery of the cake was made....paying full price was NEVER in the plan.  Mom knows her daughter....she is the one "fanning the flames" on her now grown adult child's bad behavior.  It was well known, in fact anticipated, that a PUBLIC FIT OF EPIC PROPORTIONS would ensue, embarrassment would be involved, and "magically" a lesser price would be paid.

Use this experience as a learning tool.  One that empowers you, not embarrasses you.  It has NOTHING to do with your skills or talents!  It has EVERYTHING to do with how to handle bad behavior from a generation of spoiled, feeling entitled, believes the world owes them everything citizens.

Use it to help you realize that if you don't get paid (whether it's "in full", "half the balance due upon delivery", etc...) that you should NEVER feel that you are "doing something wrong" by removing the cake and taking it back.  Add a clause, if you use a contract, (and maybe you should) that ALL deposits are NON-refundable as they are used to cover expenses involved in the creation of said cake, whether or not the cake is accepted at delivery.  (if not accepted, like in this case, leave WITH the cake and keep deposit.  If accepted, remaining balance is paid in FULL and cake is left.)

Hope this helps