Did you save any of the shiny metal parts and look at them under a microscope? Did you check them with a magnet even? Do you know if anyone ever added oil to this engine and had the foil seal fall into the motor, and you are finding the ground up bits now? As mentioned, have you even put an oil pressure gauge on it and seen what the pressures are?
If you have not even bothered to see what the oil pressure is how can you decide that a car that isn't even yours needs a new engine? Also, if you have rebuilt engines before I am curious as to why you think it needs a new one instead of replacing the oil pump and inspecting the crank journals?
I suspect you need to focus more on the relationship with your girlfriend and less on her car.