In the above query when we are trying to combine two or more tables it is necessary to use joins and specify the alias name for description and date (that means, the table from which you are fetching the description and date values)
SELECT DISTINCT Description, Date as treatmentDate
FROM doothey.Patient P
INNER JOIN doothey.Account A ON P.PatientID = A.PatientID
INNER JOIN doothey.AccountLine AL ON A.AccountNo = AL.AccountNo
INNER JOIN doothey.Item I ON AL.ItemNo = I.ItemNo
WHERE p.FamilyName = 'Stange' AND p.GivenName = 'Jessie';