Why is my cat obsessed with shadows and light reflections? Is it OCD?

It's pretty widely accepted that dogs can develop obsessive-compulsive disorders associated with lights, but it's not so recognized in cats. However, I'd say that it sounds like your cat may have developed something like this. Some suggestions I've seen with dogs that have worked is to sort of interrupt the OC cycle by offering a food reward to sort of break the fascination with the lights. Be careful not to offer too many treats as this can lead to obesity, but you can certainly just use her regular food in this game. Also try to limit exposure to light sources, and certainly don't contribute to the obsession with laser pointers. Try to find other games she might be interested in, such as ball-chasing or perhaps those toys that have a ball that goes around a track around a circle that the cat can bat at.