I was re-reading the series, and Kyoukai's healing abilities were mentioned earlier in this arc - in chapter 501, where she jokes about a technique to share life force energy with Shin, in chapter 587 where she's summoned to Ouhon's tent to provide special medical aid, and they credit her healing techniques with getting Ouhon back up on his feet in chapter 601.
and I vaguely recall her abilities in this area being mentioned in much earlier chapters, too. So this isn't coming totally out of nowhere, is what I'm saying.