"Mary did not keep it quiet at all."
Translation:Maria nu a tăcut deloc.
I would see the Romanian translation (Maria nu a tacut deloc) as being fine for "Mary did not keep quiet at all." Is there a way to signal the 'it'? Perhaps with "Maria nu i-a tacut deloc?"
The suggested translation is not very close, indeed. (I would not say it's strictly wrong because of the multiple contextual meanings the verb a tăcea can have.)
"Mary did not keep it quiet (at all)." = Maria nu l-a ţinut secret (deloc). (l- denotes a masculine or neuter object) or Maria nu a ţinut-o secret (deloc). (-o denotes a feminine object)
A ţine ceva secret is actually the Romanian counterpart of the synonymous English expression to keep something secret.