I say go with a vintage club racer theme on your modern Mini.
Polished Minilite Rims and a flag painted on the white roof is very 1960s competition Cooper. There was a factory supercharged option for the BMW produced Mini, you can probably find one for your car from someone who went either to a bigger SC or a turbo.
If she wants a different color, British Racing Green (there are several shades of it actually) is a nice choice. Or the old FIA- Spec American white with blue stripe paint scheme (British cars were green, Italians were red, French cars were light blue, American cars were white with a blue stripe). Either could be modernized with pearls, metalflakes etc. A gumball for numbers on the side and 4 driving lights are almost required in my opinion LOL Fender flares and a 2.25" exhaust tip minimum. Oh and some sports suspension will make that thing into a go kart. Some vintage inspiration: