What is the authority that should be followed to determine the beginning of the month of Ramadan for a Muslim woman residing in Zambia, given the presence of communities that follow different countries?

The people of each country must sight the crescent moon and rely on their own sighting, not on that of other countries, due to the variation in moonrise. They must complete the count of Sha'ban if they do not sight the crescent. If there is someone in the country who is responsible for moon sighting, then they must be followed. Otherwise, they should follow the sighting of the nearest country to them.