Cute sprite! I've done some modifications-
1) I think you're using too many colors. When I say too many colors what I mean is you have colors that don't really serve a purpose. It's a fairly small amount but I think the palette could be further down-sized. Too many colors that serve a similar value purpose it's just unnecessary. Also, not enough saturation sprinkled in there for my taste.
2) Break the line. With pixel art we're limited to a very small size typically which means we can't make a line thinner than 1px. So in order to give the illusion of an even thinner line you can simply get rid of the outline. At this size it's so small adding an outline can make a shape look fatter than you want it to be. You can also use SelOut (selective outlining). You'll see Boktai use this technique of breaking the line and it works quite well.
3) Give more importance to areas of interest and less important to areas that are secondary. As you can see, most of my color variation is higher up especially on the head and hair. The hair gets 5 colors for instance and there's more detail. The eyes and head have a lot of color too. Meanwhile the legs are practically black except for the addons she has (I've also made the legs skinner like in her original art).
4) Simplify! I think this sums up really what I was doing, it's one of the reasons I changed the bird's palette completely. In art, but especially at small resolutions like this, you want to make sure you simplify and verify the audience knows what it's looking at.

Hope it helps. 

PS This is a bit of a sloppy edit so you may find some small errors (like a pixel sticking out on her pants). I wanted to do enough to get my point across but that was all. Hope to see it finished it looks nice.