A couple of thoughts...
1. The word "sting" is completely misused here on TER. If you remember the movie "The Sting", the necessary ingredient that makes a play "a sting" as opposed to just being a setup is the "double cross" aspect of it. If LE runs an add on BP, and you reply to it, set up a time to meet, and are busted on arrival, that's not a sting, that's simply a bust.
What makes a sting a sting is when a real provider gets busted, and then is coerced into "turning"... She accepts additional appointments with real clients, who then get busted... And she does this as a way to get a reduced/eliminated sentence out of fear that the consequences of being arrested for prostitution are worse than they actually are. It's the "flip" of the provider that makes it a sting. Just wanted to get that off my chest, not that it will make any difference.
2. As to your UTR... There is no way that, based on a call from hotel management, that LE will just come knock on the door and arrest you for making monkey noises behind closed doors. At that point there would be absolutely no way to prove that money changed hands, etc. I agree that LE is often given way too much latitude, but initiating an arrest without probable cause creates a lot of potential risks for LE. So there's very little risk on that front.
The real risk to you is the sting... the kind of sting I mentioned above... LE sets up an appointment with her... She gets busted... they twist her arm into "turning" and taking the appointment with you... They have your emails and/or monitored phone calls as probable cause you are a bad boy, and then you get arrested when you arrive.
If she really is UTR, (and isn't the type that will appear to the check-in clerk to be under age or coerced) this is very, very unlikely.