She was fined €100 after she admitted taking the letters at her home at Aras Na Cluaine, Clondalkin in January last year.
Garda James Muldowney told Dublin District Court he was investigating the theft of post from letterboxes at the complex when he received information that the defendant was in possession of some of the missing mail.
He searched her home on January 8, 2011, and found post belonging to several other people.
This included four Christmas cards belonging to one man and a cheque for €1,000. The accused was questioned in connection with the theft. Horgan had 10 previous convictions, including three for theft, but had not come to the attention of the gardai since the incident.
She was unemployed and had one child, her lawyer said. She apologised to all concerned and was embarrassed to find herself before the court.
Horgan was in a "darker place" in 2011, having been a drug addict, her lawyer explained.
The bad practice of post lying around had developed and the accused picked some up and placed it in her apartment.
She was now on a metha-done programme. "She is here today as someone who no longer suffers from the addiction that had her in that place," her lawyer said.
He went on to ask Judge Michael Walsh to be as lenient as possible.
The judge convicted and fined the defendant.