The charity wants to present the minister with first-hand evidence of the way it thinks trade policies imposed by rich nations make life worse for people in poor countries.
"We're going to expose her to something she's not seen before - a human face of what happens because of these policies," said a Christian Aid spokesman.
Hewitt's agreement to take part in the trip is seen as a Christian Aid coup by other development agencies. With other agencies, it is preparing for a summer of campaigning in advance of the summit in Cancun.
Groups including Action Aid, the World Development Movement and Christian Aid claim trade and investment decisions taken at the World Trade Organisation can harm farming and exacerbate poverty in the developing world.
Publicity stunts, campaign events and postcard mailings are planned to try to persuade British and European ministers to put the needs of the poorest people before the interests of large corporations.
"We're going to be highlighting the fact that the push for the extension of World Trade Organisation powers are not wanted by society, or by developing countries," said Marlene Barrett, head of campaigns at the World Democratic Movement.
The group has launched a 'Cut the Corporates out of Cancun' campaign, calling on supporters to cut out newspaper adverts that illustrate corporate lobbying on trade, and send them, with letters of protest, to Prime Minister Tony Blair, trade secretary Patricia Hewitt, and Romano Prodi, president of the European Commission. The World Development Movement also plans publicity stunts outside the UK trade department during the summer.
"We are issuing a challenge to the World Trade Organisation to behave in a more democratic and accountable way," said Barrett.