I'm not sure how to interpret her words. To me it felt like gaining those powers caused her to become cripple. You could be right. The group would have to be put into a series of dangerous situations though to trigger it since Kana's power is a passive.
Actually.. active/passive gives me an idea. How about this: In order to receive forecasts for the people she cares/knows about, Kana has to remain a cripple. That's why Kazumi said "You could move if you wanted to", and Kana told her to keep quiet.
Kana willfully remains a cripple to keep her friends posted.
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edit: Wait, or was my "realisation" what you were going for in your post Neo? I associated "hanging up" with overuse, but I forgot that you've got the button as well. Given that Kana can't move though, I'm not sure whether she could hang up on her own accord.