A source close to the family told the Herald last week the bullied boy probably just "snapped".
The sister claimed that if her concerns had been noted by the school the "tragic incident" could have been avoided.
"I don't agree with what [my brother] did to the poor student, but I know that if my concerns about my brother were taken into consideration, this whole incident could have been prevented."
The ministry confirmed yesterday that her complaint had been received and passed on to the police.
"Ministry staff had now spoken to the woman and have forwarded her complaint on to the police to investigate," said Katrina Casey, ministry head of sector enablement and support.
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"If any matters relating to this bullying complaint are outstanding once the police investigation is complete, we will work with the school to ensure they are appropriately addressed."
A police spokeswoman confirmed police were given the complaint: "It has been forwarded through to the investigation team. They will process it accordingly."
Detective Inspector Dave Lynch said yesterday that the woman's little brother had still not been interviewed in relation to the stabbing.
"Police and CYF specialist interviewers have completed interviews with a number of children who witnessed the incident," he said.
"The 11-year-old responsible has not been interviewed at this time."