In a statement, the family said they “would never be able to comprehend what Nikki went through in her last moments and that will never leave us”.
They added: “We will never forget Nikki, how could we, she was the centre of our world, she was the one who made our lives so special and nothing will cast a shadow over that.
“Our girls will get the support they need from the people who love them the most.”
Assistant Chief Constable Peter Lawson said his force would like to thank the community for its support during a “hugely complex and highly emotional” investigation.
He said that while the outcome was not what “any of us wanted” it would at least provide some answers for Bulley’s loved ones.