She evaded reporters as she left court, accompanied by two men who yelled obscenities at waiting media.
Inquiries into Serenity's death took months as detectives pored over evidence and called in overseas forensic pathologists to assist after "areas requiring further investigation" were identified.
Serenity, who had just learned to crawl, was found lying in her room with eyes half-opened at the Havelock Rd home she shared with her mother, uncle Drew Scott and Ellery.
She had severe brain injuries, a broken rib cage and genital injuries.
Two days later, on April 28, family members surrounded her at the Starship in Auckland as her life support was switched off.
Last night, Ellery's Whatawhata grandfather - who helped to raise him and told the Herald last year that his grandson was innocent - said he was in shock and could not believe what had happened.
"I probably will go along to court but we don't know what's happening ourselves at the moment. We are very shocked," said Mr Ellery, who has cancer.
Cherie Kurarangi-Sweeney, a former neighbour of Ms Scott, said she was pleased to hear of the arrest.
Ms Sweeney, who started Nark (Nation of Advocates for the Rights of Kids) as a result of Serenity's death, was at her Ngaruawahia home on the day the infant was found injured.
She could hear Ms Scott arguing with her brother Drew, and lots of screaming.
"We would like to congratulate Waikato police for securing the evidence to make the arrest. It's fair to say that we have been waiting for this day for a very long time."
