Parvo infects RBC precursors in the marrow which can cause aplastic crisis in sickle cell patients.

To go through the other answers:
A and C) If she had some sort of hemolytic anemia caused by antibodies (i.e. positive Coombs test) or she had hemolysis, her reticulocyte count would be elevated B) No need to do a electrophoresis, you know she has sickle cell E) She has an elevated MCV, so she can't have iron-deficiency anemia

Healthy people who get sick with parvovirus may have a subclinical illness with athralgias as the only symptom. But sickle cell patients and patients with decreases hematopoiesis will develop[ bone marrow failure because the virus affect the hematopoietic stem cells leading to aplastic crises and inability for the bone marrow to adequately compensate hence the low reticulocyte count. parvovirus causes..slapped cheeks in kids hydrops fetalis in fetus, aplastic crises in sickle cell and arthralgias in other patients.