4yo niece often complains of sore tummy. she never has much of an appetite. she's slim but was born at 26wks. i have coeliac whats chances she has it?

Celiac genetic risk : She definitely has a greater risk than the population at large given family history. She needs to be seen by her pediatrician and bloodwork for antibodies drawn. If her celiac antibodies are elevated she will need a biopsy as you know to confirm diagnosis. Definitely do not delay, and dont take her off gluten before the tests are done! Best of luck! My daughter has it as well!