So sorry to hear your young one is dealing with this. My daughter is now 15 and has had it about 3 years. She has trie different treatments, including "watchful waiting." She had 2 very bad reactions to ivig - so I understand your concern -- but Mia has not had a bad reaction to ANY other medication (except for predinsone, which makes her hungry and cranky just like it makes everyone else who takes it.
So Mia has done in order:
Anti -

didn't really work
Ivig: bad reaction but gave her several weeks each time
Rituxan: has had 4 rounds of this two times. first time gave her 9 months remission; 2nd time gave her 10 months. (Will probably try one more series of the Rituxan in March 2015 with the hopes she'll be able to go on a student trip this summer out of the country.)
NPlate: since September. Keeps her at about 100K. We are now doing the weekly injections at home.
I think it's difficult to give our kids these drugs. My husband and I -- and our daughter (because she is 15 and also must be on board re: any decision re: her body) have gone through rather long discernment processes for each of these protocols. We aren't just willing to try what's next just to try it, especially with the Rituxan and NPlate. I think every family has to come to their own decision in their own time. I do worry about the potential long-term effects of these drugs (and there are few if any longitudinal studies on this), but we are also so grateful they give Mia a reprieve from the ITP. She responds to the drugs and, in this, we all know she is fortunate.
I wish I could give you more concrete advice, but of course I cannot. This is a hard disease in that there are no absolute answers. Every family just has to do the research and then make the choices that are best for them. For some families this is a decision not to treat. We are all here to support on another, and I will always write you back.
LAST BUT NOT LEAST: please remember that ITP is often acute, esp in younger kids, and can resolve naturally, on its own, within the first 6months to a year. I hope this is the case for your daughter!!1
Keep us updated.