Bush said she had wanted to see progress in Afghanistan ahead of a June 12 Paris conference, where Kabul will present a $50.1bn, five-year development plan for the country.
"I'll be attending the donors' conference in Paris later this week and so really want to take this opportunity to be here and to see how things have changed since I was last here," Bush told reporters.
She also announced after talks with President Hamid Karzai that Washington would spend $80m over five years to support the American University in Kabul and the government's National Literacy Centre.
Karzai said after meeting Bush that the Afghanistan National Development Strategy was a "realistic re-evaluation of the past years of our achievements, of our progress, of our problems and our objectives for the future."
The plan says much work has been done since the 2001 ouster of the Taliban in a US-led attack opened the way for international development assistance, but the level of destruction after three decades of war had been underestimated.
It asks donors to fund an ambitious plan to lay down infrastructure needed to develop the country's weak economy.
The US first lady started her trip, her third to Afghanistan since the removal of the Taliban, in the central province of Bamiyan, home to the ancient statues of Buddha that the Taliban destroyed months before they were toppled.
The Al-Qaeda-influenced movement had labelled the statues as "idols."
New Zealand troops in Bamiyan for the Nato-led force providing security across Afghanistan performed the famous haka for Bush, and she visited a US-funded police training centre and other projects before returning to Kabul.
The United States is the main backer of Karzai's government, stumping up about half of the roughly 70,000 international soldiers in the US-led and NATO-led coalitions helping battle an insurgency directed by the Taliban.
Washington has also provided most of the development aid that has flooded into the country since the Taliban were removed.
Despite international efforts and the growing strength of the international and Afghan forces, extremist unrest has grown steadily over the past two years.
Sixteen people were killed in a wave of unrest around the country Sunday as authorities announced they had found the body of an Afghan reporter for the BBC a day after he was kidnapped in the volatile southern province of Helmand.
"Abdul Samad Rohani went missing in Lashkar Gar, Helmand yesterday. His body was found this afternoon. He had been shot in the head," the BBC said in a statement.
It was not clear who was behind the attack, which appeared to be the first killing of an Afghan journalist this year. Five died last year, including an Afghan reporter who was beheaded by Taliban insurgents in Helmand.
In other violence on Sunday, Taliban rebels ambushed a police convoy on a main road in the central province of Ghazni and killed six policemen, the interior ministry said. Two civilians were killed in the crossfire.
In another attack blamed on the Taliban, a district deputy governor and three of his bodyguards were killed in an ambush in the eastern province of Khost, provincial governor Arsala Jamal told AFP.
Elsewhere, Taliban fighters ambushed a police patrol in the southern province of Uruzgan early Sunday, killing one policeman, while two Taliban died in Helmand when a mine they were planting in a road exploded, police said.
Conflict-related violence in Afghanistan left 8,000 people dead last year, 1,500 of them civilians.
Karzai is Afghanistan's first democratically elected president. He has the difficult task of steering the country towards democracy in a process mired in violence and corruption fuelled by a booming opium and heroin trade.
His term ends late next year, although he is expected to stand for re-election.