Thank you all for the feedback!
I agree that her skin should've had some texture. The thing is, my friend requested a painting that looked as close as possible like the photo he sent. The skin in the photo was almost flawless (because it was a little photoshopped), which is the reason why I didn't add texture by using a brush or layer.
But, I'll keep all of this in mind next time. I think I'll continue using this kind of colouring technique, because I like how the colours blend togheter. :]
~Lene
http://lenechristin.deviantart.com/