It was too early to say whether the Chadian refugees would start returning to their homeland, where the situation is now calmer, she said.
The UNHCR and UN's World Food Programme (WFP) are expecting to distribute food for up to 30,000 people on Saturday.
WFP trucks are en route to Cameroon, and the agency is also flying in high-energy biscuits from its regional emergency warehouse in Ghana, Christiane Berthiaume, a WFP spokeswoman, said.
The UN Children's Fund, which puts the number of Chadian refugees in Cameroon at 52,000, said the refugees' humanitarian needs were huge.
"Clean water is lacking and sanitary conditions are particularly bad at Kousseri," Veronique Taveau, spokeswoman for Unicef, said.
More than 160 people are thought to have died in fighting in Ndjamena, after an opposition alliance in 300 vehicles stormed the city after a three-day drive from the country's eastern border with Sudan.
Chad has accused Sudan of backing the rebels, a charge Sudan denies.
A senior UN official warned on Friday that a reported proxy war, being fought by Sudan and Chad through rebel groups in each country, could broaden into a regional conflict.
Jean-Marie Guehenno, the UN under-secretary-general for peacekeeping, told the UN Security Council that the situation had been exacerbated by the recent violence in Chad.
"The potentially destabilising regional implications have been highlighted by numerous media reports of Chadian rebel movements receiving support in Sudan ... and Sudanese rebel movements that have acted in support of the Chadian government," he said.
"Continuing accusations by both governments of their support for rebel movements on each side of the border increase the climate of mistrust, fuel tensions between the two countries, and once again demonstrate the potential for a conflict of international dimensions in the area."
In Ndjamena on Friday, turbaned troops patrolled the streets in pickup trucks, some with mounted machine guns.
Troops stopped cars, checking people's identification cards.
Half the shops in the city remained shut, the Reuters news agency reported.