you don't need one.
I treated my 7D minimum as bad as my iPhone. Both have no scratches on the Glass. But the 7D has... well, lets call it patina - everywhere else. Its not that there is no black color left on the body, but I am constantly working on that
The display glass is pretty good.
I will never understand how people want to look through cheap plastic for 2 years just to get 20 Bucks more when they sell the camera. I prefer looking at my pictures in the best possible quality and have fun with my camera instead of being extremely careful and thinking about what I could get when I will sell it one day.
Its made for taking pictures. There will be wear and marks, no matter how hard you try to avoid it.
Its like... a woman. Having real fun leaves minor or bigger scratches, sweat, sticky blotches,...depending on your preferences, perhaps. But unavoidable.
I hope for your girlfriend that you don't think about her value after a possible breakup when you turn off the light in the evening