Identifying an Unknown Blood Type
The passage:


  To test these samples, the only materials she has at her disposal are
  a sample of type A red cell suspension and the serum from type A
  blood.


means, I take it, that she has available two containers: One has red blood cells from a known blood-type A individual suspended in a neutral fluid such as saline solution.  The other container has blood plasma (without red blood cells or fibrinogen) also from a known blood-type A individual.

These should be enough to determine the blood types of four individuals  from the unknown test tubes (four pairs of test tubes, each pair being one with cell suspensions and one with plasma, coming from four individuals having different blood types).