It is unusual, but not unheard of. I honestly believe many kids never get dianosed because parents feel like the bruising is a result of sports or just wrestling with siblings or other activities. There are so many acute cases as well that it may come and go before anyone has a chance to really worry.
We noticed our daughter (diagnosed at

had alot of bruising and some petechaie for a few years before she was diagnosed. She also had alot of bloody noses. We just thought she was an overactive girl and bruised easily. When the petechaie appeared, we would push on it and ask if it hurt and she said no. Even one tme, she had a blood blister in her mouth and we thought it was gross-looking, but it didn't hurt, so we ignored it. (This may be a scenario that some parents may go through and just don't think anything serious is happening because their child "feels" fine.)
Anyways, one of Caitlin's 5th grade teacher's daughters had ITP. Caitlin was diagnosed in the 3rd grade so it was a relief for her to meet another ITPer. Then that same year, another boy (ironically, someone she really liked the entire 4th grade year) in her class came up to her after being out of school for a week, and asked her if she had ITP. When she told him yes, he said he was just diagnosed with it and had gotten out of the hospital after having treatment for internal bleeding. I had bought several of those "Got Platelets" bracelets and I gave them to the teacher's daughter and this boy. Then we also found out another girl in Kindergarten that year had it. So, there were 4 cases of ITP in one school. Which was surprising when they say 1 out of 10,000 kids have ITP.
I hope your daughter continues to respond to IVIG and I hope her friend wll find something that works for her. I hope you will direct them to this PDSA website. I really felt comfortable asking some stupid questions in teh beginning and it really made me feel better knowing that while this is a scary condition, it is something they can live with and have a normal life with the exception of some restrictions when the counts become real low and there are more symptoms.