Do we think it may help if I offered a few hundred bucks tip to the person behind the rental desk?
I doubt that person has discretion. There's probably a dynamic pricing algorithm that's charges walkup customers an arm and a leg during this time frame. Once you passed the 24 hours, you're a walkup customer as far as their system is concerned. People behind the rental desk and in first response call centers are like robots and have to just follow the rules.
On one of my Calgary trips I forgot to tell the rental car company I had cut my trip back from 10 days to 6. The counter people would not adjust the rate. My only option would be to cancel the existing reservation (remember I had not paid in advance), then make a new one. But of course the new reservation would have been a walkup rate, so I was better off paying for the 10 days I had reserved in advance.
Sbooker should be calling the car rental company, demanding supervisors up the food chain until you get someone with decision making power. Then you explain that:
1) You were not just a no-show. You called to let them know of your situation during the time frame you were supposed to pick up the car.
2) You offered to have Kylie's aunt pick up the car within that time frame.
3) If they won't honor the original reservation given points 1) and 2), demand a refund, and if you don't get it, file a disputed claim with your credit card company.
Then you or Kylie's aunt should investigate off site rental companies like Enterprise that do most of their business on loaner cars when people are having repairs done on their own cars.