When they ring you to ask, what happens if you insist on speaking only to staff about this? Turn it back onto them. Ask them, as you talk to them, what they think you will say. Ask them to justify any concept that she can be taken to such a place safely given her current continual breaking of the rules. Don't at any time come out and say, "I forbid it" until you feel you must, at the end of your conversation. Argue them into it. Simply say, "Given that she is constantly, clearly, using every possible opportunity to slip the leash and find someone willing to have sex with her, what precautions do you have in place to prevent this on your planned outing? If your precautions do not work, and she succeeds in getting away and has sex with a minor (male or female, she clearly is not fussy) and the parent of that minor sues, have you ensured that you are going to be able to protect yourselves legally in such an event?"
Then if they continue to indicate that she is a good kid and deserves an outing, ask them why they are asking you. if they say, "Because legally we have to have parental approval," then ask them, "And what on earth, given what I have already said about similar situations, makes you think I would give my approval? Why do you keep ringing me to ask me? Because every time you do, you make yourselves look good, and make me look worse. Kanga is not getting the connection between her bad choices, and the outcome, because you guys are not following through. You ask my permission because you acknowledge I have the legal right. So that means I also have the legal right to insist you supervise my daughter as you promised you would. You are failing at this - it is on record. Yet you still call me and ask. If you guys cannot learn, how can we expect Kanga to?"
They are dangling carrots in front of here when they know she cannot have them. That is cruel, bad for her and bad for you. They need to stop letting her think she has a chance, and certainly stop giving her false hope. To call you for permission, especially if it's after Kanga has been told of the possibility, is setting you and her up for failure, disappointment and resentment. If nothing else, get them to call you BEFORE Kanga is given false hope.
Marg