The woman, known as the ‘Angel of Woolwich’, after she confronted the killers who butchered Lee Rigby has been detained under the Mental Health Act.
Ingrid Loyau-Kennett was on a bus from Plumstead when she saw the Fusilier lying in the road in John Wilson Street and rushed to help him on May 22.
She was subsequently praised by Prime Minister David Cameron.
But it is understood she was detained last Monday by police who were called to an address in Helston, Cornwall over concerns for the welfare of a woman.
A spokesman for Devon and Cornwall police said: “On Monday June 30 following a report of a concern for welfare a 49-year-old woman from Helston was detained under the Mental Health Act.
“She was detained at about 4.20pm and conveyed to the Royal Cornwall Hospital and released into the care of the NHS.”
The 49-year-old was under police investigation following clams a Tesco worker was racially abused at a store in the town last Friday.
On the first anniversary of the killing, French-born Ms Loyau-Kennett, who received national acclaim for calmly talking to armed Michael Adebolajo and Michael Adebowale after they murdered Rigby, told News Shopper: "It was quite emotional of course to see all those flowers and tributes there.”
She added: "People say British people can be cold but I didn’t think so – it was emotional and quite overwhelming.
"Obviously justice should be done, and after that I would rather forget them [the suspects] completely."
I would say to the people of Woolwich, don’t be scared – stand up for your rights, whoever you are."