Sheska is an employee of the Amestris State Military for the Criminal Affairs office in the records department. She's a book lover who remembers everything she has ever read.
Sheska is one of the many military secretaries in FullMetal Alchemist, who just so happened to be a former employee of Centrals Grand Library before it was burned down, and assisted Ed and Alphonse Elric with discovering the components of a Philosopher's Stone.
Sheska also has a very good memory, remembering everything from every book she's read. Because of this, she was able to write and compile the notes from the book Edward and Alphonse needed. It also landed her the current job as a military secretary, recruited by Hughes to write down everything that was lost when the library burned down.