Google Play Services crashing constantly
As a last resort before resetting her phone, I saw she still had "Pokémon Go" on her phone.  I uninstalled that and the problem went away.  It must have some background services too, because the app wasn't running in the task swap view.

When I reinstalled the app, I picked her profile, and it reloaded.  The phone worked fine for the last few hours, so it seems to be resolved.