Your girlfriend should be able to do as she pleases. She should also be mindful of how her actions and decisions affects others. Freedom to choose is one thing; mindless selfishness is quite another.
This is a matter of trust. You obviously do not fully trust her, but it is not clear whether this is due to something she has done or your own insecurities. Unless she has given you some concrete reason to doubt her, you have to have faith in her.
I'm not sure what you mean by "able to hangout," but as I see it, she can do what she likes. Now, whether it's smart is another story, especially if she's serious about your relationship. It's not wise.
