Which gun does matter, some are made for compacts, some are bigger and offer more features.
As CheapTrick said, the scattergun should be the first choice, but a light on a handgun is a good option too (more precise.)
On specific lights, I can off some input, but my biggest suggestion will be on battery type. If you have nothing in your home that runs on a CR123 batteries, DO NOT get a light that requires a CR123 battery.
Also, get an LED, they run longer on the same battery and have a lower probability of not working when you need them to work.
If getting a light, consider a laser/light combo, lasers are nice for home defense as they:
1. discourage the need to squeeze the trigger
2. give confidence to aiming in high stress - especially for one without much handgun experience.
3. lasers are great blinding devices, also helps prevent the need of squeezing the trigger.
I am a fan of the X400 lights from Surefire (CR123s, but I have many things that run 123s.) They ain't cheap, but the are hella tough and have controls I like and located where I think they should be.