Police confirmed she was wearing a helmet and safety gear and was riding on a gravel driveway, not a track.
The death has been referred to the coroner and the serious crash unit is investigating.
The trail bike ride was held to commemorate Jayden Kilmister, a 15-year-old who died in 2009, after a gust of wind blew him off the back of a ute.
A tribute page has been set up for remembrances on heavenaddress.com.
Messages left for Abigail included this from Mel and Franz: "to our darling Abby, it gives me some comfort knowing that your lunch on Sunday was sitting under a beautiful tree on a beautiful day. You were so happy. You chose the pinkest stickiest marshmallow slice with the most hundreds and thousands possible. We will miss you terribly."
The family is holding a private funeral service in Lower Hutt on Friday.