Cathy - I answered in your other thread but I'll clarify things a bit better here.
When someone is first diagnosed, the doctors tend to be a little more cautious about lower counts and activities. As time goes on and they have a patient who isn't responding, they sometimes loosen up a bit, realizing that people cannot just stop their lives. They also have time to see how the patient's symptoms are and whether or not the person seems to be handling the lower counts. Many people do just fine. People with ITP tend to have larger platelets than people without ITP, and those platelets work well. There are also "platelet microparticles" which are tiny fragments, too small to be counted. People with ITP have more of those than the general population, and they also help with clotting.
If her symptoms are not too bad and she has her doctors okay, school should be alright. I worked with counts of 3 while I was having Rituxan.
Hopefully, she will respond soon. Rituxan can take some time - weeks. On the day of my third infusion, my counts were under 10. On the day of my fourth infusion, they were 150.