What do you mean, "can't"? Has she ever tried and failed?
I agree, the number should be kept small. Still, Storm could be one of those few. As I said, Storm has many common features with Thor, much more so than the vast majority of other heroes. It is likely that these Thor-like virtues are mainly responsible for making one "worthy".
I know. That's why I said: "She only lacks a notable super-strenght, but that is
not one of the requirements of being worthy for Mjolnir."
Again, do you have proof for that? Because to my knowledge, Storm has never failed lifting Mjolnir, she simply hasn't tried. And I don't mean to be rude or insulting or anything; I would just like to know if she's proven to be unable to lift it.
BTW, I posted my message on a wrong thread. It (along with these replies) should be on the "Non Thor characters who can wield" -thread.