For how many times had Elly Koss have her Systolic Blood Pressure observed?
Systolic Blood Pressure refers to DESCRIPTION = 'Systolic Blood Pressure';
SELECT COUNT(T2.description) FROM patients AS T1 INNER JOIN observations AS T2 ON T1.patient = T2.PATIENT WHERE T1.first = 'Elly' AND T1.last = 'Koss' AND T2.description = 'Systolic Blood Pressure'