illness mistaken for abuse?

Please can anyone help. When my grandaughter was 11 weeks she had a rash on her arm that wouldn't fade and later a blue black bruise appeared on the side of her head and ear. This bruise had totally faded to nothing in three days the rash took a couple of days more. Grandaughter was 8 weeks prem and nearly died, she had a bleed in the brain and has a cyst on the side of her head where the bruise was. My daughter has been accused of hitting the baby and her children are now in my care. We believe there is a medical reason for this. Can anyone suggest anything?