Storm can deal with Bobby, she's always been portrayed as the more competent of the two, even if he had a "potential" push these last few years. She's naturally resistant to extreme cold which should buy her enough time to do to him what she did to Stardust. Last time she fought a water-based guy, she just out powered his control and left him as useless water vapor. She can just will the ambient moisture away from the immediate area, taking away his resources - and we all know he won't go for internal organ freezing routs and the like.