So here's what we have right now:
It does appear to have been a (very minor, localized) stroke. At this point, hearing in her right ear seems to be returning, though the right-side facial slackness remains. There's supposed to a sort of "team meeting" with my parents and the doctor(s) in a while, so there may be more details to come, but it looks like the crisis-y part of this is over.
Also, yay for modern medicine! And thanks again to everyone who offered advice, information, and/or prayers and vibes.