Remembering when I was her age, I think I would be the same. I'd rebel against my mum at the smallest things but even more so when I was scared and angry. I'd imagine your daughter is really scared and quite peeved that she's not a normal kid anymore. And on your side of things, you're peeved because all you want to do is protect her. I also think that mainly, mums do worry much more about their children, than dads do - in general anyway.
I've found some webpages which may help you, but definitely speak with your GP or her gastro specialists about support and groups where you are. Sometimes you may find groups with email support where your cry for help is anonymous, if you wish it to be.
www.nacc.org.uk/content/groups.asp
And this is from the NACC website also - yu can call and talk to other parents who know exactly how you feel;
New Parent to Parent Service
Parent Volunteers, parents with children who have Colitis or Crohn?s Disease, have been trained to talk with other parents in a similar situation. A telephone appointment can be made through the Information Service 0845 130 2233 to talk to a Parent Volunteer. Any parent with a child who is still at school or still under paediatric care can use this service.
You're right - it's very different with us as our DS is only 3 but I'd imagine my feelings of helplessness and being out of control do match how you feel. My heart goes out to you and other parents who find themslves in these awful situations. We're meant to be here to care for and look after our children and so when something awful happens to their health, we somehow feel helpless and as though it's because something we did or didn't to.
I wish you well and hope you're able to get the help and advice you need.