well she had a few dere moments in the first seriesI thought that scene was best described as random. She's shown ZERO such behaviour towards him all this time, and right now she's even more dere than Mikoto (I'm serious)
it was a weird situation when she showed them though
touma coaught her naked in the bath and kanzaki slashed him away love-hina style.
and that blonde guy (which was way cooler in the first series than he is right know... damn "all knowing behavior") said something among the lines "thats not the way we should thank him, all he saw was your body" and Kanzaki answered "I know, but....." <---- its a bit more obvious in the series but for me that made clear that Kanzaki started to feel something for him, it sounded like she wouldn't care if someone sees her naked normaly
if I remember correctly that happened when that girl from the church in Russia came up to investigate something about Toumas father.
however, that scene in the hospital sure was over the top and I expected it to turn into a hentai scene... the way she is dressed and looked like felt more like High school of the dead than Index.