Stephen was diagnosed just before turning 17, at a children's hospital and he stayed with the ped GI until 18. The hospital was very strict with the date so we had no choice but to move as soon as he turned 18... ie had a follow up that had to be moved up by a week because it was scheduled for one week AFTER he turned 18!
I've only had relatively short times with both the ped and adult GIs (approx. 1 year with each), but I haven't found a huge difference in the quality of care and Stephen's felt comfortable with both GIs. If anything, I think the adult GI has been more aggressive in fighting inflammation. I had the sense that the ped GI was willing to allow things to 'drift' a bit since things were stable as he knew transfer was imminent (don't mean 'neglect', just, perhaps, hesitant to begin a more aggressive treatment he wouldn't be following up for the long term).
I've also found that the IBD clinic at the children's hospital was so BIG, that you were almost just a number in the line-up of the clinic's patients! While the adult GI is also based in a large hospital/large IBD clinic, Stephen seems to be more a patient of the specific GI, not of the clinic. (... if that makes sense??
) If anything, I actually would have expected a bit more of the opposite...
The adult GI was recommended by our ped GI.
Something else to consider, as I said, our children's hospital was very strict re 'age'. There was a girl at the ped clinic who was turning 18 within days and required surgery. The ped GI had to make a special request to perform the surgery and keep her for a few days following but, within a week, she was transferred to the adult GI/hospital. So, if your children's hospital is strict with age/dates (but, from what's above, seems your med system is more flexible), you may want to make the transfer to a new GI while she is feeling good so you don't find yourself in a situation where she is ill, perhaps requiring a new treatment and you are then in the middle of a transfer.