Every sympathy with Kate and hoping she can recover and take part but for her to say in quote saying that she thought it was just poncing about in a dress is ludicrous.
This is really really bloody hard to do. People seem to think they can literally just walk into dance training 6 hours a day. They cannot. My fitness is good but not as good as two years ago when I did the Inca Trail in Peru. I trained hill walking and in a gym for 5 months. Even then, it was immensely hard.
Dancing for that amount of time is very very demanding. It is one reason why sportspeople do so well. Whereas a lot of showbiz types sole form of exercise is propping a bar up as I well know.

The average age of people doing this is the wrong side of 35. The kids on SDF were regularly crocking themselves at 18.
It should be mandatory for the celebs to do a specialised fitness programme for 2 months before they even put dance shoes on. I'm not saying injuries can be avoided but it'll improve the stamina if nothing else.