Fun Fiesta Cakes ...
If it’s any consolation, your design was very pretty! I would have called the client back and offered to either return the money or give her a full credit for her next cake. Perhaps that would help ease your disappointment and hers.
At the risk of repeating the same thing, I am almost positive you had a structural problem. I have a rule of thumb when I do multi-tier cakes – I use as many dowels as the width of the cake – if I have a 10"cake, I use 10 dowels — if I have an 8" cake I use 8 dowels and so on.
Dowels come in wood, plastic, straws, etc. They also come in different widths – the thicker ones, I use on the bottom cakes because of the weight. They are all good, as long as you place them properly on your cake. Always dowel your topper – even if you think it’s too light to cause any damage.
One last thing – refrigerating your cake won’t damage it – as some of the other ladies have mentioned, just make sure you don’t touch it because fondant will sweat. The good news is that it will eventually dry and it will be as good as new.
Good luck and chuck this up to experience – you’ll do great next time.