It depends where she is going.

If she's going to a night club, then I would tell her not to go. But if she insist, then I'd ask her if I can go with her. And if she doesn't like that idea, then I would call it a problem coz there's gotta be something wrong there. And it aint about trust, jealousy, or insecurity.

Best thing you should do is to TALK with her about it.