Looks great so far. Since you're looking for critique, I would recommend using a harder brush for your highlights and shading, airbrushing tends to make things look flat. When you shade, pick out a light source before you start and think about each shape as a 3D object and think carefully about how the light will hit it. Also (this is a bit of an advanced concept) when you're picking colors for shading, try to avoid a darker version of the base color, think about what color the light source is and what colors could be reflecting off the environment. For the hair on her head, it looks very nice, but it doesn't have a definite light source, you don't have to shade every individual hair, think about the shape it makes collectively. As for the hair on her tail, if it's going to be that long, there's going to be stray tufts that interrupt the smooth outline, think about how hair behaves on a real tail to know where to place them. For the background, I realize it's not finished, but when you do start on it, don't put grass right up against a body of water, whether it's a pond, lake or beach, there's always going to be some kind of bank or cliff in front of it. Grass doesn't grow in heavily saturated ground.

I used Photoshop, not SAI, so I actually did use a hard brush except when blending on her clothes.
My light source is 10-O-Clock but there is also reflection from the water.
For my shades I picked blues and purples, and my highlights I picked oranges and pinks. I realize this maybe hard to notice since her clothes are cool colors. (And the fast I used multiply on the shadow layers and Luminescence on the Highlights)
Since her hair is a lighter color it requires more detail, and her hair is also more than one color so I had to show the darker strands, Her hair is a Silvery Lilac/Lavender color with Blue-Violet tips and undertones, her highlights are pink, and low-lights blue. Hair is also a very reflective base especially in sunlight.

I will admit I could add more contrast to her clothes.

Her tail I am having a major issue with, the fur strands are supposed to be long, but I'm having an issue with making it look like fur.

Stray hairs will not come into play until I do the final touches, since I still need to shade the grass and the water. :3

I did not put in a bank because if you look at her hand's position she is on a ledge hanging over the water. I was planning on making the water dark near the ledge. I realize as it is this detail could possible not be noticed. :3 but in fact I need to contradict you about grass not growing in wet spots. Have you ever been to a marsh or probably a swamp? Sometimes when I go camping I will unfortunately step into wet soggy ground thinking it is a solid grass patch. :3 Not all grass it the stuff we have on our lawns ^w^

Thank you for taking the time to critique my WIP btw. I really appreciate that you chose to comment.