- Which model of MacBook Pro? Or at least check System Profiler to see whether you have a Broadcom or an Atheros-based card.
- What version of Mac OS X?
- When her wireless cuts out, do the AirPort menu signal strength bars go to zero?
- What is she able to get back on the network just by re-selecting it from the menu?
- What kind of security are you running on that network?
- Have her hold down the Option key while clicking on the AirPort menu while on the network. What channel does it say?
- What RSSI does it say?
- What firmware version do you have on your Time Capsule? (Check the actual number, don't just say "the latest". People who say "the latest" are usually wrong.)
/var/log/system.log say when this happens?
Try turning on AirPort debug logging, reproduce the problem, and then see what the logs say:
sudo /usr/libexec/airportd debug +AllUserland +AllDriver +AllVendor
You can turn those debug flags off later by running the same command, but with the plusses turned in to minuses.