Is there a chance that RCL will allow my 11 1/2 year old as she says "level " up to be in the kids club with her older brother.
I can not tell you for sure yes or no, but I would say there is a pretty good chance they will let her age up a group. Keep in mind that your 11 year old would be leveling up to the Teen club. The teen club is run differently then Adventure Ocean. For example they do not have set hours they are open, The kids just pick and choose what events they attend, and they do not have to be signed in or out. You know your child the best, so you know if these are things she is ready for or not.
Your best bet is to talk to the teen councilors on the first day. In the past some people have said they had to sign a waiver to let there child younger than 12 participate in the Teen activities, but I am not sure if that is still the case. Either way I recommend they go during the first evening on board as that seems to be when most people meet the people they end up hanging out with for the rest of their vacation.