Hello, you've requested a critique, so I'll give you a quick one with some pointers and compliments. ♥
The character is clear to see and it is easy to see what you have drawn. It would have looked better if the image was cropped more, to have your character stand out more and have less empty space at the top and right.
I have not watched Invader Zim, but Kin looks very original.
(I'm not sure if she has pants or socks, I'm going to say pants, so correct me if I'm wrong. orz)
The stripes are very nice, though they could have looked better if you drew the stripes on the pants closer together, to make the top and pants look more unique from each other, and if the stripes were more consistent in spacing.
Putting the pattern aside, the little bow is adorable. ♥
Not sure if you use a mouse or tablet, but both benefit from the inking/pen tool. They keep the lineart more stable, smooth and gives you more power of how much weight they have.
Your coloring and shading is very good, your shading could be a little bit darker though to have it stand out more, but it still looks nice.
Kin looks very static, she could look a lot more fun if they were doing something or posing with an expression. Or something that is a crowd pleaser is reactions. Does she like books? Would she read it, throw it away or burn it? Maybe all three? What if a dog were to lick her. Would she smile and hug him or be disgusted and shove them off? You decide.
I used to do backgrounds just like that, they look much better than a solid color or a gradient blend, but the problem with doing backgrounds like this is that the character sinks in with the background and the character is just ignored, drawing an outline around her or using drop shadows make a huge difference and makes your character stand out more.
Hoped that this critique helped, have a nice day.