The jealously you feel is normal and stems from a fear of losing her. However, you cannot succumb to this jealousy because you cannot control her actions and it will interfere with the trust that is between you.
She should be capable of doing what she wants... and it is up to her to take your feelings into consideration or not. You cannot force her to do this... no matter how much you would like to.
All relationships are built on trust... trust that the other person won't leave, cheat on you, or hurt you in any way. If she were to go on this trip to Las Vegas... you would be expected to trust that she will not cheat on you.
If you were to force her to stay and not go on such a trip... then she would view you as controlling, distrustful or her, and possibly crazy. This would be very bad for your relationship and could even lead to its ruin.
You can tell her how it would make you feel if she were to go... tell her in a kind and considerate way. She could take this into account... but it's up to her to decide what she will or will not do.
Learn to control your jealousy... it can destroy relationships if left unchecked.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen