si arthritis

My daughter (15) has just been diagnosed with crohns and si arthritis.  Is this arthritis the same as AS

Thanks for replying. She had an MRI. She has been having back pain for around two years. When it first started we had an x ray-which showed nothing, then we had a full body scan which also showed no abnormalities. She went to a physical therapist for about 3 months and that helped a little. Then came the stomach problems!!! Once she was diagnosed with crohns and we talked to the doctor about her back problems (I never put the two together) he ordered some kind of blood test called HBL 27 (or something like that). That came back negative so he said she did not have arthritis. The pain never went away so I asked a friend of mine (who is a physician) to order an MRI. The radiology report said she had inflamation in her SI joints and called it arthritis. I had read a few things about AS and I stopped because it scared me. She also complains constantly about her joints (knees mainly) hurting and popping. We just started seeing a pediatric rheumy and GI that are in the same practice. Problem is they switched her meds to a sulfa drug---she had a horrible reaction---which threw her into a crohns flare that she cant kick. She is now on soooo many drugs!!!! And still feels like a dog! Way to much for any 15 year old!!! I guess knowledge is power and this website has been a godsend for me. Thank you so much!