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.