It was a revelation that put to question the police communication channels because Mary's family said they had filed a report in Kibera around that time.
It would take 15 years for the family to see Mary again, thanks to a story published on March 26, 2017.
Nation Media Group journalists led her Kibera family to Dagoretti on April 2, 2017, where the teary reunion happened.
The young girl identified herself as Sabrina Adam, but Ms Wanjiku found this name to be quite a mouthful and so she named her Mary Njeri.
For 15 years, she had been following the Christian ways of Ms Wanjiku's household, but her original family was Muslim.