BEGONE, THOT!
And what a dirty way to force him into meeting her, leaving him her ring that she could very well call out stealing—even if it was just a cheap piece of plastic—if he doesn't come to the next show to return it. Best thing to do here, imo, is be up front with Urumin about the meeting and return the ring through her while keeping himself faithful to his oshi, but I highly doubt it will turn out that well. At the very least, talk to Urumin first and warn her ahead of time before confronting the skank.