Some ideas for you - firstly, I assume your friend has checked with the airline company who may have a separate insurance arm. Secondly I use insurance provided by my bank account. The main international banks are hard to find in Malawi but if friend still has a UK bank account, or needs to open one anyway, s/he may find this has travel insurance or could be upgraded to do so.
Next, contact the travel companies in Malawi - Land and Lakes or similar, just check Lonely Planet on line. Or contact Geo Group, the UK Tourism agency for Malawi who will give you contacts. If you are not into computers maybe phone Geo Group?
I am going back to Malawi in July, and can't wait to be warm again even in the winter time there!