Her family described her as having been "full of life" and "generous of heart".
The 60-year-old was originally from Norwich, Norfolk, before retiring from her job as a road safety officer with Norfolk County Council. It is believed she moved to live in Tenerife. She had two daughters and five grandchildren.
Her daughter Sarah said yesterday in a statement: "Mum retired a number of years ago and was fully enjoying her retirement travelling between Tenerife and France where she spent time visiting her daughter and grandchildren, and her other daughter in Norfolk.
"She was full of life, generous of heart, would do anything for anyone. We now have to find a way of living without her love and light."
She died on Friday when she was attacked in the Valdes Shopping Centre in the tourist town of Los Cristianos.
Witnesses spoke of their horror and disbelief after she was stabbed and decapitated in a supermarket.
The attacker was said to have carried Mills-Westley's head outside and was reportedly saying "God is on earth".
Last night, a Foreign Office spokesman confirmed that consular assistance was being given to her family and offered condolences to them.
Reports named the suspect as Deyan Valentinov, who is believed to be a homeless Bulgarian man with a police record.
He is understood to have obtained a knife from inside the store to launch the attack and was later arrested.
Colin Kirby of Tenerifemagazine.com, who was in the supermarket at the time, said: "There were people shouting.
"There was a Hispanic-looking guy walking behind me, looking very scruffy, muttering to himself, carrying what I thought was a joke head by the hair. The blood - it just made me think Clash of the Titans.
"I thought, 'The guy's a nutter, it's a joke'."
He added: "The security guards came out, they chased him across the road. By this time he's empty-handed.
"They got him on the other side of the road, just by the cultural centre. A couple of people tried to get him, they flattened him, got him on the ground."Kirby said he had spoken to an English couple who were in the shop at around 10.30am on Friday when the incident happened.
"They said this guy just walked in, pulled a big knife and started stabbing at her," he said.
Christina Perez, a legal representative at a nearby court, said a group of lawyers saw the man exiting the Chinese shop, carrying Mrs Mills-Westley's head.
"They saw the man running out of the supermarket with the head in his hands," she said.
"A security man from the complex ran after him and jumped on to him so he fell, and then he threw the head on to the road."
Perez, 38, said her frightened colleagues darted indoors for safety.
"They were shocked. Some of them ran to the office and locked themselves in," she said.
"Everybody is shocked. It's a very safe area. You can usually go anywhere you want in the day or at night. This is really not normal."
Dominica Fernandez, of the Regional Interior Ministry, said the attack appeared to be random and that the suspect was well known in the area.