Does it bother you that is going without asking you? If so then her behavior needs to be addressed as crossing a boundary.
If you are Ok with her going say, "Have a good time." Then make sure you are taking care of yourself. You need to book a night out with your buddies and don't ask.
Cheers
M22,H45,W45 S21/18D12 Retain faith that you will prevail in the end, regardless of the difficulties and at the same time confront the most brutal facts of your current reality, whatever they might be.
