I've known plenty of JWs on anti-depressants. They don't qualify as happy. And just because a group of people can force smiles and claim that they are happy, doesn't mean that any of it is sincere.
I'm not sure if I understand your situation well enough to give advice. Are you showing interest in JWs because you're interested in this JW girl? If it's just a matter of your family, you only need to plan a fade.