Are you sure she's a mix? She looks like she could be a purebred siberian husky to me (they have pure white ones) just on the small side...I've seen some that small before.

Here's a page with pictures of white siberian huskies http://www.huskycolors.com/white.html

I doubt samoyed or shepherd as they are larger dogs, american eskimo is possible. Whatever she is, she is GORGEOUS!!