Thank you for all your comments, it is really useful to hear what you've experience in this situation and that for some of you it has only been a one time occurance

There are two things that could have quite easily triggered it, one is when she got onto the kitchen table at my mum's house and she nicked about 4 cup cakes with butter icing on them and I gave her a marrowbone from the vets and it had quite a bit of fat on it - ignorance not bliss in this situation

. It is also encouraging that some of you have not continued with the vet precription foods, that is something to think about long term.
Daisy is looking and acting a lot better today although I think I gave her too much Lactlose yesterday and when she went to the toilet this morning it was shooting out like a jet, poor girl, but at least her tummy is emptying and she is looking less bloated so she must be feeling more comfortable. I think she might still have a temperature and she was panting a bit this morning, but she is going back to the vets tomorrow to check her over. She is on anti inflammatories and antibiotics.
It is so worrying when they look so poorly and you don't know what is wrong with them.