I have my own cake business so I'm going to chip in.
I'm going to defend the cake maker here.
The covering of the cake is really very good and I like the bottom tier. It's not like your picture tho I will admit.
How was the conversation left with her regarding design? Did she say she would do her own take on it? It's very hard to paint on icing and it's a real skill, I know this as anything similar to that is above my skill and I give my cakes like that to a artist to do the painting side.
The top tier is really ugly, who came up with this design for the top?
The sugar craft flowers are lovely.
The cake is leaning, could be a number of factors transport cake not dense enough to take the weight.
Did the cake have dowel rods in?
To me this cake looks like it's been knocked as I've seen cakes that hasn't had dowels in and they tend to sink in, that damage is at the bottom.
If the design is not what was asked for I would concentrate on that as in my opinion that damage does look like it's taken a hit.
Did you sign anything on collection? As I make my customers sign a contract stating they are responsible for transport and any damage done after left my house is their responsibly.
However if this was my work I would say a partial refund as a goodwill guesture upto £50.