She would need to discuss that with her doctor. When low platelets occur during HCV treatment there are no medicines available at this point to increase the count. I have heard some mention trial drugs but that should never be a consideration during pregnancy. Of course, they could always tranfuse her if she became too critical.
"Very low"? What is her platelet count? A low platelet count is a symtom of an underlying condition or illness. What disease(s) does she have? Hep C? Liver disease? Some other condition? She needs to treat the cause of the low platelets.
She should see her doctor about this as low platelets can indicate a serious illness.