"With the signing of the Good Friday agreement, my generation, the children and grandchildren of the civil rights protesters were told we would be the first to enjoy peace in decades", she wrote.
"Those who brought guns onto our streets in the 70s, 80s & 90s were wrong", Democratic Unionist Party (DUP) leader Arlene Foster said on Twitter.
"The senseless murder of Lyra McKee has left a family without a beloved daughter, a sister, an aunt and a great-aunt; has left so many friends without their confidante".
"It is equally wrong in 2019. My thoughts are also with the courageous officers who stood in defence of their community", she tweeted.
Ms McKee was highly regarded by her friends and journalistic colleagues, who took to Twitter to mourn her death on Thursday night. "The blame for last night lies squarely at the feet of the British Crown Forces, who sought to grab headlines and engineered confrontation with the community", it said.
Speaking in Dublin, Irish Prime Minister Leo Varadkar said the people of Ireland and Northern Ireland had chosen peace and cooperation 21 years ago and will not be "dragged into the past" by political violence.
Tánaiste Simon Coveney added: "The news from Derry is shocking and tragic". They draw their inspiration not from the shared, tolerant, pluralistic future that Lyra McKee believed in deeply, but from a past where grievances are nursed like pints. "I can't imagine life without her, and yet now I must".
At a vigil in Derry, Sara Canning said she had been left without "the woman I was planning to grow old with".
The deal led to the decommissioning of weapons held by the main militant groups, the withdrawal of the British army from Northern Ireland and the creation of a power-sharing government.
The National Union of Journalists (NUJ) described McKee as "one of the most promising journalists" in Northern Ireland. Police have blamed dissident republicans and the New IRA in particular.
A burning vehicle in Creggan, Londonderry after petrol bombs were thrown at police.
"A single gunman fired shots in a residential area of the city and as a result wounded Ms McKee", Hamilton said.
She was rushed to Altnagelvin Hospital in a police land rover but was pronounced dead a short time later. She fell at the wheel of a police vehicle.
The trouble comes after the announcement on Monday that "Soldier B" will be prosecuted for the murder of 15-year-old Daniel Hegarty in the Creggan area in July 1972. "Sick to my stomach tonight", O'Neill tweeted.
Mobile phone footage purporting to be from the scene shows at least two shots being fired before a distant scream is heard.
And if that gunman is honest, he'll turn to his son and say, "I shot a wee woman in Derry".
The Derry unrest came just before the Easter weekend when republican dissidents traditionally mark the anniversary of the 1916 Easter Uprising.
He said she was a "perfectly innocent" bystander with legitimate reason for being there but had not been "actively working" as a journalist on Thursday evening.
A young journalist was killed in Northern Ireland overnight in what police are treating as a "terrorist" incident.
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