Hyatt was 16 when she bled to death after being stabbed near her neck during a house party in Peachland in 2010.
On Saturday, a jury acquitted the accused of second degree murder.
On Sunday, the jury found the accused guilty of the lesser charge of manslaughter.
As the verdict was read, court sheriffs had to calm cheers from two dozen of Hyatt's family and friends.
Charrie Hyatt, Ashlee's mother, burst into tears of relief and joy.
"I can't even explain to you how I'm feeling. Two-and-a-half years of waiting and believing and praying that she would have to be accountable for her actions and I am just very thankful that she has to be," Hyatt said.
Hyatt also said she was content with the guilty verdict on the lesser charge.
"I'm okay with that. I know there really isn't much difference between second degree murder and manslaughter other than intent. And I don't know if she intended to or not but at least, you know, she has to be accountable for her actions."
Samantha Weller, one of Hyatt's best friends, had some mixed emotions when the verdict was read.
"I wish it was second degree, but I'm just happy it's something, 'cause Ashlee deserves something. She deserves more, but at least it's something that that girl has to pay for a little while anyway," Weller said.
Metres away from the family, the accused woman stood in shock, and then broke down crying.
She had testified that in a scuffle with Hyatt and another girl, she had only punched Hyatt.
Because the accused was a minor at the time of the incident, she can not be named.
The jury also found her not guilty of assault with a weapon and assault causing bodily harm for an alleged attack on another teen girl at the same party.
She remains out on bail in the care of her parents until a sentencing hearing, which will be scheduled once a psychiatric assessment and pre-sentencing report is completed.
Crown lawyers have said they are seeking to have the teen sentenced as an adult.