My wife has trouble with her boots digging into her shins, she has got slim legs so it's not that. It doesn't matter if she wears them loose or tight, she gets the same thing, we hire our boots and she has tried 2 different types, neither were any good.
i remember from my judo days that some people have shins that run like a razor blade. a very prominent bone line running down. try more padding at the front.
She usaully has to fold up an extra sock and put them in behind the tongue of the boot, this helps a bit but she can't ski all day as pain gets too much!