Where did she remember putting the case when she put on her glasses to read? I assume that she did not touch the case again until she finished reading.

Was anything moved round in the study by anyone apart from the lady reading? If so what did they move, where did they set it down, and did anyone replace what it was that was moved. Could the spectacle case have been inadvertently lifted by someone moving something else, and left behind when whatever it was that was moved was replaced?