I have a pair of Lakes that I just love. So far all I have had to wear under them is one pair of wool socks and my feet were fine last winter for up to an hour or more, depending on how much I had to walk in the snow.
Just have her try on different styles/brands till she finds one that is comfy. Get it a size or two bigger. This way you have room for thicker socks, but you also want some air and wiggle room which will help keep her feet warmer. This way you can add those toe heater things if needed too. Make sure they are waterproof.
Just my 2 cents.