Write SQL query to solve given problem: For how many times had Elly Koss have her Systolic Blood Pressure observed?. Keep the solution inside sql tag ```sql [SQL-Query] ```
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'