The normal form is to accept the request to have your picture taken a bit impassively, and then pull the face of your choice. She looked very grumpy in the picture but was dead keen to see her image on the camera. Apparently you have to show the photo you've taken as otherwise it's seen as rude.

There is nothing tribal about this face paint, though it has become quite iconic of this area as it's so striking. She is wearing the paste from the root of a plant which softens the skin. It's a beauty treatment. But flaunting that you're undergoing the treatment in public is normal, and the girls wearing this seem self conscious but proud when they are snapped by photographers.