Malala Yousufzai flew out of Pakistan on Monday morning, nearly a week after Taliban gunmen shot her and two classmates as they were on their way home from school in the northwest.
The Pakistani military says Malala will require prolonged care to fully recover from the physical and psychological effects of her trauma.
The military says she will need to repair damaged bones in her skull and will require intensive "neuro rehabilitation."
Malala was shot in the head. Doctors at a Pakistani military hospital removed the bullet and stabilized her condition.
She was shot by the Taliban for promoting girls' education and criticising the militant group.
Tens of thousands rallied in Pakistan's largest city on Sunday in the biggest show of support yet for the 14-year-old girl who was shot and seriously wounded by the Taliban for promoting girls' education and criticizing the militant group.
The October 9 attack on Malala Yousufzai as she was returning home from school in Pakistan's northwest horrified people inside and outside the country. At the same time, it gave hope to some that the government would respond by intensifying its fight against the Taliban and their allies.
But protests against the shooting have been relatively small until now, usually attracting no more than a few hundred people. That response pales in comparison to the tens of thousands of people who held violent protests in Pakistan last month against a film produced in the United States that denigrated Islam's Prophet Muhammad.
Malala earned the enmity of the Pakistani Taliban for publicising their behaviour when they took over the northwestern Swat Valley, where she lived, and for speaking about the importance of education for girls.
The group first started to exert its influence in Swat in 2007 and quickly extended its reach to much of the valley by the next year.
They set about imposing their will on residents by forcing men to grow beards, preventing women from going to the market and blowing up many schools out of which the majority were for girls.
Malala wrote about these practices in a journal for the BBC under a pseudonym when she was just 11. After the Taliban were pushed out of the Swat Valley in 2009 by the Pakistani military, she became even more outspoken in advocating for girls' education. She appeared frequently in the media and was given one of the country's highest honours for civilians for her bravery.
The military carried out its offensive in Swat after a video surfaced of a militant flogging a woman who had allegedly committed adultery, which helped mobilise public support against the Taliban.
Many hope the shooting of Malala will help push the military to undertake a long-awaited offensive in the Pakistani Taliban's last main sanctuary in the country in the North Waziristan tribal area.
The Pakistani Taliban said they carried out the shooting because Malala was promoting "Western thinking." Police have arrested at least three suspects in connection with the attack, but the two gunmen who carried out the shooting remain at large.
The young girl was shot in the neck, and the bullet headed toward her spine. Two of her classmates were also wounded in the attack.
Doctors at a military hospital operated on Malala to remove the bullet from her neck, and she was put on a ventilator. Her condition improved somewhat on Saturday when she was able to move her legs and hands after her sedatives were reduced.
On Sunday, she was successfully taken off the ventilator for a short period and later reconnected to avoid fatigue, the military said. Doctors are satisfied she is making slow and steady progress. They have not said whether she suffered any brain damage or other type of permanent damage.
Afghan President Hamid Karzai has written letters to top political and religious leaders in Pakistan denouncing the attack on Ms Yousufzai and asking them to help battle extremism in both countries, the president's office said in a statement issued late on Saturday. Mr Karzai wrote that he views the shooting as an attack on Afghanistan's girls as well.