Sorry about your niece and the experience with the ped and GI. It absolutely is possible a child can have IBD. I know kids diagnosed at age 2. My son was 6 at diagnosis. And it is completely ridiculous to say a 5 year old is too young to be tested. The pediatrician could start with labs if they haven't, to see if sed rate, crp, albumin, hemoglobin are normal. This is how my we got the hint that something was wrong with my son. If those are abnormal, I would definitely get to a pediatric GI.
We used to live in SC before my son was born. At times I have toyed with the idea of moving back, but I noticed there weren't pediatric GIs there. If I were living there, I would probably travel to Chapel Hill.