I would probably join my child and paint with her :)

I mean what's done is done and no matter what, we can't reverse this scenario, so I'll paint with her and make sure that later on she'll clean some of those walls with me.

My next logical step would be to use the washable paint for children's room. 

Let them draw whatever they want on the wall and let the creative juice flow.

AK

I don't have children but when I was a little girl I used to paint the walls, my parents quarrel to me but I remember a did it again and again. I just can tell you that she doesn't do it because of badness, she does it because in that moment she feels she want to or need to. Even though, if you already gave her notebooks and show her where she has to pait, I thin you should put her to try to repair the wall, so she will know that her actions will have consequences and buy for her a canvas or panel where she can paint in a bigger space. 

Common sense would dictate not giving the 3-4 year old unsupervised access to paints and other things they can use to make a mess.

You get a lot of that with children. It's never easy. Even when they are as young as four, five, six years old they in a strange in-between state--you are never quite sure when they are being perfectly innocent or doing experiments testing boundaries. 

Certainly, one can put up a big whiteboard in their room and give them a way to make it OK to draw on the wall. One can try washable paint. Particularly in their own room, the rules can and should be different from the rules in the rest of the house.

Certainly, one has to accept the fact that children put wear and tear on a house! 

One thought. My wife used to give our kids regular house-painting brushes and a pail of water and invited them to "paint" the outside walls of our house with water. They loved it! The water darkens the color of the paint, and then it dries without leaving a trace. Water also "paints" sidewalks, concrete, and stonework.