Dora ist zur Party gegangen.
Dora hat es ihren Eltern nicht gesagt.
These two sentences are very neutral with regards to their respective time line.
"Dora hat es ihren Eltern nicht gesagt." can be simply understood that she never told her parents, neither before nor after the party.
The simple and correct way to build one sentence from it is as given in #2:
(1) Dora ist zur Party gegangen, ohne es ihren Eltern zu sagen.
This is equally neutral. She didn't tell her parents before the party and probably neither afterwards.
(2) Dora ist zur Party gegangen, ohne es Ihren Eltern gesagt zu haben.
This sentence presumes in addition that we focus on the fact that Dora didn't tell her parents before. This might be semantically reasonable, but is not necessarily implied.
As often with these exercise sentence, they are formally correct, but not perfectly idiomatic. German actually lives on all the small words we like to add to sentences, from tiny adverbs to flavour particles. And these additions usually make very clear, what we talk about.
Dora ist einfach zur Party gegangen, ohne es Ihren Eltern vorher zu sagen.
This would be idiomatic and the present infinitive is totally fine.
Dora ist einfach zur Party gegangen, ohne es Ihren Eltern vorher gesagt zu haben.
This is grammatically perfect, but sounds a bit elevated and stiff. In written legalese protocols this would be recommended, but not in spoken language.