The correct answer is option4i.e. When she is on a four-day fast after recovering from malaria and is taking care of someone suffering from chickenpox
A person is most likely to fall sick in this condition because
Malarial infection which is caused by protozoa has led to a large scale destruction of red blood cells (RBCs) and has weakened the immune system already
A four-day fast deprives of proper and sufficient diet which
further deteriorates the functioning of the immune system
Lastly taking care of a person suffering from chickenpox which is caused by virus and is a communicable disease makes it vulnerable to getting infected and falling sick