For pac boots, you're probably not going to get any lighter. And though I have no experience with said boots, I've never had a pair of boots that weren't at least a little stiff before being broken in, work, hunting, or pac boots. Probable depends on how they're made too. My advice would be for her to just wear them around the house for a little while, and as long as they aren't rubbing or creasing in any way that's causing pain, they'll probably be alright. But if she doesn't like them, by all means send them back. This is why I won't order boots. It's in the store or nothing.
Good luck.