Vanessa Nathakumaran says it is her "duty" to ensure she is first in line for the Lying in State.
A 56-year-old Londoner says she plans to be the first in line to attend the Queen's Lying in State at Westminster Hall - and has provisions at the ready to queue for two nights.
Authorities are warning of huge overnight queues to see the Queen's coffin at Westminster Hall.
But Vanessa Nathakumaran, from Harrow, says "it is worth it because of the Queen's dutiful service".
And she has a head-start. Mourners wishing to pay their respects can do so from Wednesday, 14 September.
London officials have already developed an extensive plan to accommodate the massive surge of people coming to see the Queen lie in state - Rachael Younger reports
But Ms Nathakumaran is already waiting. She arrived near Lambeth Bridge at 12pm on Monday and says she will spend the next two nights there, in a bid to be the first to see the Queen's coffin.
"I'm not actually thinking about the waiting time but my main aim is to pay respect and I want to be part of it," she said.
Her daughters will bring her food and a change of clothes during the day while her energy bars, which she says newspapers advised readers to carry, will help her to keep her stamina.
Ms Nathakumaran said she has no qualms about queueing outdoors, day and night, to pay tribute to Her Majesty.
"She did a good service to Britain and the Commonwealth...and it is our duty to say thank you for her service," she told ITV News.
Infrastructure is being set up and security staff are preparing for millions of people to wait to pay their respects to the late monarch, whose coffin will be placed in Westminster Hall from 5pm on Wednesday until the morning of her funeral, on Monday, 19 September.
Full details of the funeral proceedings will be released at 10pm on Tuesday.
Ms Nathakumaran said she decided to line up early because "she heard about the long queues."
The administrative assistant grew up in Sri Lanka before moving to the UK to study in the 1980s.
She said her great-uncle, Sir Vaithilingam Duraiswamy, was knighted by the Queen's father, King George VI, for services to Sri Lanka (then called Ceylon.)
"From that time on, I wanted to learn about British history and got more interested in it," she explained.
Her daughter, Praveena Nanthakumaran, met the Queen as an air cadet, she added.
Security staff and stewards are lined up at regular intervals along the expected queue route, which will stretch around Parliament, past the Lords and Victoria Tower Gardens, across Lambeth Bridge and loop back north on the other side of the river past the Covid Memorial Wall.
Metropolitan Police officers, as well as Welsh officers, are manning the expected route, parts of which are already lined with barriers.
Portaloos and crowd control infrastructure such as barriers and temporary flooring have been set up inside Victoria Tower Gardens.
A marquee and armed police could be seen at the entrance to Cornwall Gardens, with several police and emergency service vehicles parked across the road.
Security staff by Victoria Tower Gardens said crowds are expected to swell ahead of Wednesday afternoon.
They said the queue is likely to snake for miles, potentially all the way along the river to Tower Bridge.
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However, it is not clear if the queue will stretch along South Bank after Westminster Bridge or down through the streets of Lambeth.
People will not be allowed to camp and will be given numbered wristbands to indicate their place in the queue so they are able to leave and come back, security staff said.
People will be able to queue 24 hours a day until 6.30am on Monday for the Queen’s lying in state.
Commuters may want to “change their working patterns accordingly” as London will be “extremely busy” for the Queen’s lying in state, No 10 said.
Asked if there will be any facilities for people who physically cannot queue for 30 hours, he said: “Obviously we want everyone to be able to attend regardless of whether they have disabilities."
"Our focus is on ensuring they have the information needed to make the decision about what’s right for them."