German-Enlishg Translation Question (esp. Grammar)

German text: Er dachte,"Sie hätte auch nichts zu sagen brauchen." (According to the context before, she actually had said something)

My translation is: He thought,"she wouldn't have needed to say anything, either."

My explanation is: It is Konjunktiv II Vergangenheit Form "hätte...zu sagen brauchen"; although normally, the form should be "hätte....Verb im partizip perfekt Form", but here it's the modal auxiliary "brauchen". So I'm using the conditional form in English, and it is in the past tense, so "would have + Ved".

My lecturer's key is: He thought,"she needn't have said anything, either."

His explanation is: It is not Konjunktive II Vergangenheit Form. So conditional sentence is obvious wrong.

I can accept his key but not the explanation. I think "needn't have said" actually means the conditional, just as in "shouldn't have said". However, I should use the modal auxiliary properly. I am wondering if "needn't have Ved"form actually has the meaning of conditional but just with modal.