Heh... I actually just finished talking my girlfriend through this one not more than fifteen minutes ago.
You've got to make sure you've asked her about Leo, first and foremost, but I'm sure that's already taken care of. After she's gone off on a psychotic break, it's just a waiting game. You've got to keep traveling with her until you see her take her pills, and then ask about it. Then you rest. As far as I've been able to tell (and with The Vault mum on the issue, as well), there's no set trigger that makes her take her meds. It's most likely passage-of-time based once all the necessary conditions have occurred.