Marta
Google
This is my top one choice for Africa-inspired gift-shopping in Nairobi. It's not the cheapest but most frequently, if you buy cheap you are buying China, even in the Masaai Market - although you may end up buying China anywhere these days, cheap or expensive, so be on the look out for things that you see everywhere and don't have a specific made-in-Kenya label explaining the origin.
Most of the products are made by social enterprises in Kenya and they have good quality materials.
They were at Sarit before. Now they have moved a few meters away from Westgate to a less-known mall but it's still conveniently located and parking is free.