She said Congress "saved" the institution of monarchy for 60 years, "but now we are changing our minds. People have lost their confidence in the king. Nobody wants monarchy anymore."
Koirala, who said she escaped to India on a motorcycle, and other Nepalese leaders demanded the forming of a constituent assembly and fresh elections.
They said they were looking to India for help.
"There is no hope in Nepal. We need the help of India, the United States and other countries," Koirala said, while urging New Delhi to stop all military aid to Nepal.
India has been supplying arms and helicopters to Nepal to fight the raging Maoist insurgency but Defence Minister Pranab Mukherjee said last week that there was "no contract" with Nepal for regular supply of arms.