If you as a hobbyist are hosting, just go downstairs, meet and buy the lady a drink at the bar, then head upstairs.  If she is hosting, she can meet you in the lobby, bar, or outside, or she can call the desk and allow you to pick a key to go upstairs yourself.  So long as the lady doesn't have a revolving door of clients visiting, it shouldn't be a problem.

One additional note: There was one W I visited a lady at earlier this year where security was out the wazoo, in addition to the key card issue.  Despite that, I was able to meet with her without incident.  Just use your head, don't panic, and trust your gut if you encounter anything beyond your comfort level.