Is IVIG the only drug that was infused. My daughter would get the mouth sores when she was given methotrexate or prednisone, but not necessarily IVIG. So, I wonder if a different drug is causing the mouth sores?

Yes, there are comments in the literature about IVIG adverse effects that state some people have the adverse effects during infusion but others will not have the adverse effects until a few days later. You may want to do a PubMed search for IVIG adverse events to find the literature to show your docs.

I have heard that slowing infusion rates, reducing IVIG concentration, and changing IVIG brands can help alter these reactions but I have no medical training to say that.

Good luck!