Welcome to HCM
After going through history of your wife it is possible she was suffering from Malaria
as we have to treat patient and not reports, always investigations are corelated clinically ,with your details it is not clear that she received antimalarial treatment or not?
If her fever
has responded to given antibiotics it is also possible to get negative widal
in first week of fever where blood culture
is used for diagnosis.
Low platelet count
is seen in many condition including Malaria.
If platelet count is decreased keep a watch on platelet count usually it improves as disease improves.
Your Physician is best person to tell you about the disease.
Hope fully she recovers soon