angela F,
SickKids is a top-notch hospital, so I'm glad that's where your daughter is receiving her care. I hope the doctors there can soon reach a diagnosis.
Do you know if her bone marrow results showed abnormally large platelets (macrothrombocytopenia)? If so, the article
MYH9-Related Platelet Disorders may help explain why they are testing for MYH9, and presumably which of its syndromes might be affecting her.