I found a thread on reddit that implies she can be either found sitting near the cows in the Druid's grove, or she just up and left without saying anything because she doesn't like Lae'zel and can't be found again. Given I ditched her for Lae'zel (it was supposed to be a temporary thing...) I'm going with the latter in my first time through. Not a problem with the (I presume to be patched) bug allowing Gale to learn cleric spells, but once that's fixed, the lack of a healer might not go unnoticed.