It’s perfectly fine to be insecure when you don’t know the person enough to trust them. Actually it’s not insecurity, it’s because trust is yet to be established. But it’s completely her choice and you have no say in the matter. This is the truth. You can convey your concerns about safety but that’s it. If you had been dating this girl for a while and you knew each other, you could have expressed your discomfort as couples do. But in an arranged marriage it’s a different scenario. Honestly, there is a small chance that she may hook up with someone. It may be her last chance with an ex or something like that. She’s deciding to spend the rest of her life with you and for one last time she may want to have a bit of fun with her friends. I don’t know if it’s right or wrong but it’s understandable. It’s more likely just going to be harmless fun. I suggest you make sure that she is safe and not be overly possessive until you’re married. I also recommend that you enjoy yourself a little bit and don’t allow the thought of her being with someone else fester in your mind. You both don’t know each other well enough yet, you’re not in love yet. You’ve agreed to get married and that’s it. Whatever happens before is each individual’s choice. Though I suggest asking her very clearly and in person if any of her ex boyfriends or anyone who has been interested in her would be present during this trip. This is a perfectly valid concern and has nothing to do with you being possessive or insecure. However she answers and whatever she says , your instinct will tell you in that moment if she is someone you can trust. When you trust someone, you respect and relate to their values. Good luck. Go with your instinct.