It must be unbearable pressure having to make this kind of decision on behalf of a child. I am actually in awe just thinking about it and how I would feel if it were my kid. Plus, I have been there on the other side of it.
I had UC from age 9 and although no surgical decisions needed to be made until I was 29 years old, I recall the immense worry and pressure my parents felt as I bounced from one hospital to the next, 3 in total during the 4th grade. My parents are the kind of people that wear their emotions on their sleeves and during those multiple hospitalizations when I was a 9 year old, going through a lot of testing (because frankly the doctors back in 1972 did not know what was wrong and they did not have the same handle on UC as they do now), it wrought hell on my parents and especially my mother. I remember a doctor talking to my mother at Montefiore Hospital in the Bronx NY, and seeing my mother collapse in my father's arms. I learned much later on, years later in fact, that the doctor told my mother they were going to be testing me for leukemia. I probably should not have had to see this, but I did, and my mental outlook seeing my mother like that was not good.
The most important advice I can give you as a parent of a child sufferer of UC: show nothing but strength and determination to your daughter in your face, in your body language, and in your voice, even if that is not what you are really feeling. You have to be a great actress, an Angelina Jolie or whomever your favorites actress is. Kids take their cues about how their mental outlook should be from their parents, and you need to be stronger than her so that she can follow your lead.
Good luck and keep us posted on how this goes.