Jean is not the type to get scared like that. And she puts her friends first. I'm sure that Storm not being herself is what's worrying her, not whether Storm would kick her ass or not. Plus, as others have said, she may be trying to distract Storm so she doesn't hurt anyone else, and/or trying to see what she can do to bring Storm back to normal, rather than trying to take her down. Try thinking a bit about the story and how the characters feel instead of just being all "LOLOL Jean is delusional!!!! How can she think she can win against THE GODDESS!!!1". It's NOT about that...