To answer your question, AIH is not passed on to a child genetically. Actually, it is quite rare to have more than one family member with AIH. However, autoimmune diseases in general are more common in families, so other family members might have another AD.

It is important that your sister be treated by a "high risk obstetrician" if she is taking medications for AIH. Many women have had successful pregnancies while taking Prednisone, Imuran, or both, but a high risk doctor is recommended.