Please, can you take pictures of the GBA game? From all sides. It may be that it's a fake. When did you/the owner get it? Also, take a picture of the packaging as well, it's another giveaway.
Does the game have the Nintendo seal of quality on it? Please describe that if you could.(A close-up would be good, so I can compare it to mine).
If your game is legit, it's beyond me. But I have my own legit copy of Emerald, complete with 99% of its' packaging (slight fading on the game), so I hope I can help you.
EDIT: Sorry, didn't notice you p.s. But tbh, for us to be certain it's not fake, it's best to get screenshots. So if the person you're asking on behalf of could get some, that'd be really useful.