Koirala, a Goodwill Ambassador for United Nations Population Fund UNFPA in Nepal, said she will support the pregnant women, new mothers and their infants, besides trying to restore a sense of dignity to them.
"I am truly happy to renew my partnership with UNFPA in my homeland at this crucial time. UNFPA's lifesaving interventions are needed more than ever," Koirala, 44, said.
More than two million pregnant women are affected by the disaster and many of them are at a risk of unwanted pregnancies, according to a UNFPA statement.
"We wholeheartedly welcome Manisha Koirala as a spokesperson for our cause," said Giulia Vallese, UNFPA Representative in Nepal.
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"Our efforts must be sustained well into the future, and must be adequately and consistently resourced. We are very grateful to Manisha for her dedication and commitment, and look forward to working together strategically both now and in the future," Vallese added.
UNFPA, alongside the government of Nepal, is helping to coordinate and provide health services and a range of other medical facilities for the pregnant women.
The UN body is also providing "dignity kits" - containing sanitary pads, a flashlight and clothes - to restore a sense of dignity and wellbeing for displaced women and girls.
"I am struck by the impact UNFPA's work is already having in several of the most-affected districts. Dignity kits are reaching thousands of women and girls, and UNFPA's work is expanding in the days and weeks ahead," Koirala said.
"Even during an emergency it is essential that women and girls still have the choice whether or not to get pregnant, and we need to save the lives of those who are giving life. We must continue working as quickly as possible ahead of the monsoon season, which is just weeks away," she added.