If there even are fuses, relays or circuit breakers for the HVAC.
The newer TIPM's (totally integrated power modules) use solid-state drivers to turn things off when a short or other problem is detected. They should reset and store a fault code with a key off-on cycle unless the problem is still active, then the fault code will remain active.
A battery disconnect may reset the TIPM or HVAC logic if that's the problem. Otherwise it may mean a trip to the dealer for diagnosis.
The blower may have a conventional blower resistor if manual temp control (MTC). An ATC system would have a solid-state module for blower speed control.
Check for 12 volts and ground at the blower motor at the right side of the dash. Something may have opened.
If she is close to the dealer and the issue pops up again during business hours, she should stop in while the problem is still active. Nothing may show up as being wrong with the system while it's working OK and the only way that they may find anything is with the HVAC blower failure present.
Yes, it will have to go back if/when it quits. However her extended warranty will be over soon. So she will have to pay out of pocket. But we have to have AC in the Central Valley with summers hitting 110-115.
She must have a written and signed shop repair order made out with the 'no blower' concern in writing on it for any possible future protection from this when it is out of warranty.
The dealer can go through the motions of attempted diagnosis like loose connections or fault codes, but may find zilch if the problem isn't there at the time.
A spoken 'it's just not acting up now' from the service advisor will count for nothing. Even if this happens on multiple occasions. A customer may argue that they had the vehicle in for a problem many many times, but it needs paperwork to back it up. It must be documented that she took it in for this issue, even if nothing was found.
I understand the anxiety of an expiring extended warranty and the importance of getting everything fixed under that warranty if possible.
Documentation written while still under warranty is key, but no guarantee of future out-of-warranty coverage. It can only help. The Diagnostic fee may be charged for the first visit, but after that she can ask that the fee be waived because it is the same repeated problem. A service manager should be OK with that.