My DD was also born with an imperforate anus with a fistula. We were new parents and didn't think it looked right but it wasn't caught at birth. We took her to the pediatric surgeon at 2 weeks and he was livid and scared the heck out of us. Saying the baby should never have been released from the hospital should have gone right to them, etc. etc.
Anyway. At 2 weeks she had a colostomy, at 6 months she had surgery to have everything rerouted, had the fistula closed, and had pull-through surgery to create a functioning anus.
She is 10 today and she can't poop without laxatives. When she was four the Dr. wanted do to a permanent colostomy but we said no, that would be her decision to make and who knows what advances would be made in the mean time. She may have to get an irritation system someday but as long as she can manage through laxatives for now, that's how we go.
She is a thriving kid who Irish Dances, plays soccer and is our social butterfly.
To OP good luck to your friend's grandchild