Which lens to take to Africa?

I recently had a friend ask me this question. She is going to Malawi to work with girls and women, helping them with their education needs. She wants to take her camera to document her travels and is totally torn between purchasing a 31 mm f/1.8 or a 50 mm f/1.4. She needs a fast lens, meaning that it will have a large aperture to let in lots of light (ie. small aperture guide number f/1.4 as opposed to f/4.5) because many of her photos will be taken in dark huts. This situation and the need to travel light pretty much rules out any reasonably inexpensive zoom lens in the f/3.5 - 4.5 range. Following is the email I sent to her.

I've been thinking about your lens situation. I don't know what your equipment budget is, but I think you would be very happy if you could have both the 31mm and the 50mm. You could use the 31 for tight quarters where you want to take a photo with some context ie. mother with children, children playing, women working, etc. Then you'd use the 50 for when you want to get in for close portraits and catch the look in their eyes and totally remove the person from their context by blurring out the background. The two lenses have different purposes. You are taking your camera to Africa to tell a story and to bring the story of these women back to Canada. I think the 31mm lens might be the better choice for that purpose. Context is important to storytelling.