She has met with the victim's family in a group conference and apologised.
Chelsea's mother said it had been a healing experience, Stuff reported.
She had forgiven the teenager, and felt sorry for her.
"It's helped me move forward," she said. "I just felt sorry for her. All the people there for her were professionals, not her loved ones. It's pretty sad.
"At the end of the day it's given me closure. I wasn't expecting to forgive her, but forgiving sets you free."
The teenager, understood to be 16 at the time of offending, discussed her progress with a judge in the Christchurch Youth Court on Tuesday, Stuff reported.
She had admitted one count of causing harm by posting a digital communication, and two unrelated charges of assault and one of threatening to kill. One charge of assaulting her mother was withdrawn on Tuesday.
Stuff reported that Judge Jane McMeeken ordered the teen, in the care of Oranga Tamariki, to delete her Facebook accounts. The teen has started her 40 hours of community work and must attend support programmes for drug and alcohol abuse.
"You can't change what has happened in the past, but you can make the rest of your life positive," Judge McMeeken told her.
The Harmful Digital Communications Act was passed into law in July 2015, aimed at curbing cyberbullying.
Under the act it is illegal to post material online that deliberately causes serious emotional distress. Those convicted face a fine of up to $50,000 or up to two years' jail.
At the end of 2017 84 people had been convicted of offences under the act, Stuff reported. Of those, 12 were aged 19 or younger.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• The Word
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.