Police said a 49-year-old woman had been detained under the Mental Health Act.
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"She was detained at about 4.20pm and conveyed to the Royal Cornwall Hospital and released into the care of the NHS."
Loyau-Kennett was under investigation following claims a Tesco supermarket worker was racially abused at a store in the town last Friday.
"We are aware of an incident which took place at our Helston store on Friday," a Tesco spokesman said.
"Colleagues at the store are helping the police with their inquiries."
Loyau-Kennett received national acclaim for calmly talking to armed Michael Adebolajo and Michael Adebowale after they murdered Fusilier Rigby in the street.
On the first anniversary of the killing, Loyau-Kennett spoke at the scene where she checked Fusilier Rigby's pulse and confronted Adebowale.
"It has been a waste of three lives and, of course, a year on I still think about Lee Rigby's mother losing a son," she said.
"It's a tragedy. I don't have flashbacks, but I have been very emotional lately.
"This street looks like a normal street now, but I can still see the body, see the crashed car and see the bloodied hands."
Adebolajo, 29, was given a whole life sentence, and Adebowale, 22, told he must serve a minimum of 45 years' imprisonment at the Old Bailey in February.
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- AAP