I've never heard of someone so young having such a severe case. She's gone through so much already. Biologics are the heavyweights in terms of medications.
It sounds like you will have to resort to Remicade or Humira at some point. The azathioprine that she is on may work, but it can take up to 6 months to reach effectiveness. She would likely have to remain on a Prednisone wean until it reaches that.
It sounds like they are awaiting the metabolite test result to see what the most effective dose will be for her.
I hope and pray that she gets back to good health soon.
Tom.