The United Nations mission established to monitor Nepal's peace process, Unmin, is scheduled to leave the country on Saturday amid uncertainty about its future.
The mission is closing after Nepal's warring political parties agreed not to extend its mandate last September.
In a last-minute compromise deal, the government and the Maoists have agreed to take over the UN's monitoring duties.
But there is still some uncertainty over how the peace process will continue.
Established in 2007, Unmin monitored the arms and personnel of the Maoist army and the Nepalese Army under a peace deal that brought 10 years of conflict between the Maoists and the state to an end.
It also helped conduct elections to a Constituent Assembly in 2008, in which the Maoists won most seats but fell short of an outright majority.
But despite these successes, Nepal is still a long way from concluding its peace process and writing a new democratic constitution.
"I believe we could have done more given a different mandate," says Ms Landgren.
"It's been frustrating having the monitoring end of things without being able to influence the decision making."
Many of the conditions of the 2006 Comprehensive Peace Agreement have yet to be fulfilled.
The Nepalese Army has not been restructured. More than 19,000 former Maoist fighters remain in cantons around the country, their weapons under UN supervision.
A deal to either integrate them into the security forces or rehabilitate them into civilian life has stalled because of distrust between the Maoists and an alliance of the Nepali Congress and the Communist Party of Nepal (United Marxist Leninist).
The peace process in Nepal has been deadlocked since the collapse of the Nepali Congress and CPN-UML coalition government in June.
Since then, the country's parliament has held 16 unsuccessful votes to chose a new prime minister.
A 17th vote was cancelled this week after the only candidate standing, the Nepali Congress MP Ram Chandra Poudel, withdrew.
It is hoped that this will pave the way for a new power-sharing government, which will move the peace process forward.
All the parties agree there is no alternative to consensus. But there remains deep division between them.
The Maoists had wanted the UN to stay.
"Unmin has been a psychological deterrent on both sides not to break the peace process," says Maoist Vice-Chairman Baburam Bhattarai. "Without it there could be trouble."
But the Nepali Congress and CPN-UML disagreed.
Some in these parties feel the mission has always been too close to the Maoists, and resent its equal treatment of the former rebels and the state security forces.
In this respect they are backed by India, Nepal's large and powerful southern neighbour.
India, who is fighting a war with Maoist rebels within its own borders, has played a key role in trying to exclude the Nepali Maoists from power.
It has also had a behind-the-scenes hand in advising members of the UN Security Council that keeping Unmin in Nepal would only slow down the peace process.
"India sees any foreign presence in the territory of Nepal as a possible challenge to its hegemony," says political commentator, C K Lal.
"This is because India interprets the 1950 Indo-Nepal Treaty of Peace and Friendship as a special relationship between the two countries - and thinks that India has special rights over foreign policy in Nepal."
As Unmin prepares to withdraw its staff, it has said it will maintain a close relationship with Nepal.
The country is set to write a new constitution by the 28 May but with political attention focused on who is going to be the next prime minister, it is looking increasingly unlikely that this deadline will be met.
But Ms Landgren says she believes that the gains made during the last four years will not be reversed.
"It's up to Nepalis to pull up their boot straps because time is very short."