Basically you follow the following steps:
1. Prime
2. Color paint
3. Clearcoat
The details get more complex. Usually you want to get it painted in a spray booth, which has a special ventilation system so that dust doesn't get on your paintjob. Barring that, a garage with a fan can work pretty well. An airbrush or spray gun is the best way to apply the paint, but you can do a pretty good job with automotive spray paint from a local auto parts store like Pep Boys. Dupli-color is a popular brand and they color match many cars on the market.
For the first step she will need to prep the body kit by sanding and then priming. Make sure the primer has sealer in it. Do a 2 or 3 coats of primer. Sand the primer after it dries and start applying the color paint. Sand between coats, but don't sand the top coat. Next spray on the clearcoat. Do at least 2 or 3 coats of clear. If you want a mirror-finish, wet sand the top coat of clear with really fine-grit (like 2000) sandpaper and then use a polishing (rubbing) compound and wax. There's no magic in painting; it's all about prep work and patience.
