Keying and double matting?

So I have a shot of an actress against a green screen. She is well lit.

What I would like to do is have her silhouette "filled with stars" and the background behind filled with another image (lets call it lava).

Not even sure this is possible.

My first attempt: keyed out the green screen, inverted the matte, put the star field behind the clip. Looks great, but the green screen is now a pale white color. Made this a compound clip.

On that compound clip, I key out the pale white color and put the lava behind that clip. It almost works, but because there's a lot of white in the "filled with stars" clip I am using, a lot of lava bleeds through the stars because I keyed out the "white" green screen.

Is there another way of doing this?

I feel like i need to create two mattes somehow, with the stars under the first matte, and lava under the second. But how?

Thanks!!!