She is not very ill. But I have had to have her home from school all the last week of term, and she is missing other things now. 
Have tried a few bits (some homeopathy since that has worked for us in the past, and also rehydration salts which she hated) and went to the doc on Weds. They said if it carries on bring in a stool sample, which I will do tomorrow, but I don't know what else to do.
She is not dehydrated as she is drinking lots and weeing lots. She is having accidents in her pants as she can't tell when she is going to go. Sometimes it is just clear mucus in her knickers. Sometimes the poo is yellow, sometimes brown, sometimes hardly anything. None of the rest of us have caught anything. Mystified.