Generally speaking, there is no difference between the lower shell of a men's model and the equivalent women's model. Feet are feet, and women's feet come in all shapes and sizes like men's do. The only real difference in shells will be the sizing, as women's shells tend to start at 22 and men's with 24/25. Dalbello has a new boot this year where the women's shell is 1mm narrower than the equivalent men's, but this is not necessarily true that all women's feet are narrower than men's...
The main differences are in the liner and cuff, particularly in the height and calf shape of both. Typically, the cuff is lower and more sculpted to make room for a woman's calf muscle which is usually lower than a man's of the same shell size. Sometimes companies use thicker & softer foam in the liner construction, but not always (nor is that always a good thing).
But as it always comes down to fit, it could be the case that a unisex boot can fit a woman better than the "women specific" version. For example if a woman is trying on size 25 shells, she could try on both men's and women's boots to see which cuff better matched her leg. Typically, the women's design is a better match, but not all the time.
