just some ideas
-condo, apartment, duplex, or single family home (switches/timers from other areas controlling the ckt) ?
-how long has she lived there (does the br light turn off the plug and she doesn't know that) ?
-recently divorced/spiteful exspouse ?
-dead spouse that was handyman ? (look for hidden timers that turned things off at night)
-power company power saver, water heater timer, appliance timer that's wired wrong or bootlegged into that ckt ?
-does she have 240 at the main ? (ckt backfed thru water heater when its on cause she's missing a leg?)
-it is possible some harry wired a crazy 3 leg or used the neutral on a 3 leg in an adjacent room, and some crazy hallway or closet switch is turning it off. If you really want to trouble shoot it, tell her if it goes off not to touch anything at all and call you to make a service call. It would be nice if she kept a log - what time it went off and what was the last switch or electrical item she touched, etc, to help you figure it out.
-next time it goes out if you still can't figure it out:
a) find everything that is fed on that circuit, trace wiring if possible
b) turn off everything but the breaker feeding that, check to see if there is another breaker in the panel that is backfed, trace everything out on that circuit
-swap the circuit it's fed onto another breaker, and lock it out. don't tell her the locked out breaker is the one feeding it, tell her it's feeding something else but you want to check it. put tape on the breaker that it was fed on and tell her not to touch the breakers. tell her to take a pic of the woody when it goes out. see if she messes with the taped breaker. if she's a nut case the locked out breaker will drive her nuts and/or she'll find a new problem, which may or may not be real since you've swapped the ckt.