i went in 05 and getting lucky is always an issue. either you or her must be staying at non inclusive hotel. we were at the clipper club, and within days, it was known as party central cause we could have anybody over at any time either that or pay the security off. they aren't real police and are wide open to bribes. $20 american dollars to the guy at the door, usually was enough to get into any hotel late night. they won't do it during the day though because of the free food and drinks, its easier for everyone to be caught
try sneaking someone in to a room with that extra arm band can cause you problems too. You really do not want to stay in the local jail in Cancun due to your trying to beat the system.
As someone that lives in an area that realies on tourism money, and having many friends that own and operate hotels for a living, these common threads annoy the hell out of me. Heres some advice. If you can not afford to go on vacation, DON'T. What you are trying to do is NO different than stealing. Stay home.