Well without a police report or even a direct statement from RG herself it is just a rumour. And since it is about someone who is present and accounted for, it's a dangerous rumour to be spreading around the internet IMO. It's a little different than rumours from first party witnesses who claim to have been told something directly by the victim or POI themselves I think. It appears that this is pure speculation on the part of the friends.
I also agree with Just-a-Guy. People who abuse alcohol and/or drugs have a much higher incidence of injuries than other people. She could have simply fallen and broken her arm, or had to be detained somehow to prevent further injury. I wonder what she said happened?
MOO
It's called libel and if it were me, I'd be talking to an attorney.