Do you mean decorative ones, similar to alessandro? He uses nail polish. With other colors it's hard to get it even and without it wearing off, ususal choice is spraypaint with multiple layers. You can also dye white ones, there are a quite a few people who have tried it,
heres an interesting thread on DT for example.
If you won't be dyeing them you will lose the legends and I wouldn't try to paint them on again, they are simply too small to get a decent result.
I would let her try it on some caps from an old rubberdome first and then get some blanks, look at the vendor forum, you have a huge choice so choose whatever is cheapest for you.
