First Prius issue the day I leave

Hello,

I departed the US on business so my wife decided to use my car while I was away for a few weeks. Keep in mind, I have never had an issue with my beloved 2008 Gen II prius. So, after 18 hours of flying I get to my destination and check my e-mail which stated that she needed to have the car jump started and to call when able to get the details. Bad things such as battery cross-polarization immediately crossed my mind. I was finally able to get to a phone and call home. Her depiction of what happened is that after 2 hours of shopping she returned to find the car horn sounding, as it does when the panic button is hit. However, she had to use the actual key to enter the car and inserted the FOB before the car horn ceased.
When she tried to start it, it wouldn't start so she called our emergency roadside service who assured her that they would have someone who knew how to jump a hybrid come out to assist. Of course, and without fail, when the wrecker driver opened the hood he looked at her and asked where the battery was. She then had to get the manual out and walk him step by step how to jump the car. Thank goodness she actually listened to me for once about the hazards of letting someone jump it.
It took almost a half tank of gas before the traction battery displayed any readings of power. It is now back to full bars. She still doesn't know what happened. I can only guess that she somehow inadvertently hit the panic button while in a nearby store and the thing sounded for 2 hours. So I have some questions for you guys:

1. Is there any other reason why this could have happened? She swears there was nothing else left on and I don't see any other way.

2. If it was the panic left on, is there no timer to shut it off after so long? Or low voltage cut-off so that it can't drain both the 12V and the traction battery?

3. Was there any possible long term damage done to the traction battery by it being completely drained?

Thanks for the help. I'm on the other side of the globe and worried about my Prius

 

Thanks for the replies all. I get now that the panic probably ran down the 12V and the traction was recharging it over the half tank of gas. We live in extremely hilly terrain and stop and go traffic. She may have exaggerated with respect to the actual gas required to drive until she got a reading. I'm going to check the 12V when I get back home.