How many times has she done this?? At least a few times, quite easily in fact. If you need the proof, I can post a scan or two, but I'm not just making this stuff up....not really my style.
How does she actually do this?? She manipulates anything that's electricity, which includes electrical impulses that carry information through the brain. She can literally suck the electricity out of a person, rendering them a vegetable
And Storm can't block it because?? I dunno....because Jenny's living electricity? Maybe she can, but has she ever displayed that kind of defense?
Also, I've never contested that Storm has way more versatility.....but harming living electricity is hard (like I said, unless Storm could manipulate Jenny herself, which remains debatable and pretty much un-provable either way). Energy like that can't just be destroyed easily.
So it's either a boring stalemate or Jenny wins.