I have an update. The doctor came to see her mid morning. Good news and bad. Good news is that it's not bronchiolitis as there has been no downward descent of mucus since she has been in. Te other good news is that although she is eating a little less than usual she has put on weight each day she has been in, and is not dehydrated. And the final good news is that when she is given paracetamol the fever comes down to something almost normal.
The bad news is that she still has fever and they won't let her go until it either comes down of its own accord or they find out what it is. So they finally agreed to run tests, and this doctor listened to what I said about why I didn't consider her breathing to be related to a cold as she always been like this. I's nice when they listen as he just said right, well, she's young, was born early, could just be compensating for slightly weaker lungs which will improve as she gets bigger and stronger. I should keep an eye on it and continue seeing the paed regularly as we already have planned. I just wish they had listened to me before as I told them the breathing had been like that since birth and that she can't have been born with a cold !
He bollocked the interns for not running tests on admission, but they were just following protocol and convinced themselves it was bronchiolitis 
So I am at home now and when I left they had just taken a blood sample and attached a bag to her to collect some urine. When the doctor comes round this afternoon they should have basic results which should tell us if there is an infection. If there is she stays until full results are received and they can start treatment. If nothing is flagged up we'll assume that her temperature is related to the cold she has had and send her home with instructions for treatment and what to look out for. DD1 had a cold a few weeks ago which ended with four days of raised temperature, so it could just be the same virus which would need to run its course.
Bt I'm feeling positive. She seems a lot better in herself today, and as I said, if there wasn't the temperature she'd already be home. But I understand that they want to keep her in until they know what is causing the temperature, and at least rule out serious infections.
I wandered around the corridors in the ward today when LO was sleeping and some of the very scary stuff that children in there have really puts things in perspective.. Of course things can turn very quickly into something serious for a new born, but she's in the right place so there's nothing I can do except wait for them to decide she is fit to come home to us.
Hope to have some positive news tonight.
Thanks again for all your good wishes.