Hello,
Thanks for the query to H. C. M. Forum.
Celiac disease is diagnosed her younger sister so note down following things as,
Environmental factors play an important role as
gluten present in wheat,rye,barley,oats.
2 Immunological components ,
3 Genetic factors.
As you mentioned that biological father is same so chances are more of celiac disease.
Broad spectrum antibiotic with
folic acid tablets are the best treatment ,but consult a physician and get in treatment.
Hope I have answered your question.
If further any question I will help.
Best wishes for your daughter.
Dr. HET