Along with a bee emoji, which is a symbol of the North West England city, she wrote: "love u v much".
Twenty-three people including the attacker were killed in the terror attack at an Ariana Grande concert.
Meanwhile, Prince William remembered the 22 victims of the Manchester bombing by attending the Manchester Arena National Service of Commemoration at Manchester Cathedral, according to the reports.
The 24-year-old singer took to social media to send her love and warmth to the people in London through a series of tweets.
Prince William read from Corinthians during a service full of song and tribute to the victims and their families.
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Yeah, Fortnite always tracked your performance across matches, but now it's putting its V-Bucks where its stats are. Epic today announced the next limited-time game mode for Fortnite , and it's called Solo Showdown .
Thousands of people paused outside Manchester Cathedral at 2:30 p.m. for a minute of silence that was observed across the country, including in Parliament, where lawmakers paused their debates and fell still.
In an article for the Manchester Evening News, Theresa May said: "The targeting of the young and innocent as they enjoyed a carefree night out in the Manchester Arena on May 22, 2017 was an act of sickening cowardice".
"It was created to strike at the heart of our values and our way of life in one of our most vibrant cities, with the aim of breaking our resolve and dividing us".
The cathedral service was shown on a big screen in the city as well as in other cities across Britain, including York, Liverpool and Glasgow.
Twenty-two concertgoers were killed, and police say more than 800 people were left "with physical and deep psychological injuries".
'Horrific' school bus crash in New Jersey
The bus was transporting students from East Brook Middle School in Paramus, New Jersey, according to a school official. Officials said the bus driver is a district employee, and the school bus is owned by the Paramus Public Schools.
The youngest person to die was just eight years old.
Later on thousands - many of them youngsters - gathered in the city centre for a "Manchester together" concert, with performances from local youth choirs, poetry and recorded messages of support from celebrities including former Manchester United star Ryan Giggs.
Bells were scheduled to ring out from the town hall at 10.31pm, marking the moment the attack took place.
Oil traders, Keep An Eye on the UK Brent Crude Oil
Oil's rise to $80/bbl is stoking concerns that the price rally will erode demand, but OPEC's giants so far aren't anxious . At 432.4 million barrels, US crude oil inventories are in the lower half of the average range for this time of year.