On the serious side:
Costco, Sams, Wallyworld I have seen the $100 wireless camera setups. Many of them mount on license plate like a frame so no drilling. This would give her an actual view of what is there with distance. Some vehicles it's REAL hard to tell how close you are and also effected by person's height.
"In October 2005, “Consumer Reports” measured the blind spots — the spaces behind a car, van or SUV that a driver can’t see — for the Honda Accord, Dodge Grand Caravan, Toyota Sequoia, and the Chevrolet Avalanche, using toddler-high traffic cones.
The results were eye-popping. The blind spots ranged from about 12 feet behind the sedan for a person of normal height (17 feet for a shorter driver) to about 51 feet for a shorter driver behind the biggest vehicle, the Avalanche." The Villages Daily Sun
I can tell you that I was able to put my Corolla within 2 inches of bumpers/cones etc front and back. My Sonata I swear i'm close but am like 2 feet away just because of drop off. My Sequoia (see above) with me backing it up (my wife is 6 inches shorter) at 15 feet backing into my driveway all you see is the roof line of my Sonata (was the same for my Corolla) I added the Rostra obstacle sensing system
Rostra Precision Controls, Inc. - Automotive/Consumer Products - Rostra Obstacle Sensing System to the Sequoia. It mounts BEHIND the bumper cover so you see nothing and no holes. Beeps as you get closer (like an RD signal strength) AND the LED's change from green to yellow to red. I mounted the LED's above the back window. While looking backwards, you hear the beeps and see the LED's. By her own admission in the first week it saved her twice from backing into something low. System was $300 installed at the time, insurance deductible was $500 if she hit something. At about 1 foot it goes to solid tone. Great investment IMO for the safety side nevermind care of vehicle. I've been backing up when the kids were out playing and I can see them 20 feet away. All of a sudden the alert starts beeping so I stop quick. It turned out to only be the basketball that rolled but how fast do the kids chase after it?
Camera type from Rostra
Rostra Precision Controls, Inc. - Automotive/Consumer Products - RearSight Back Up Camera Systems