Key cards should never be an issue if the lady is discreet.
Many carded elevators have over ride codes, and most ladies are familiar with what they are.
Meeting in the bar is not a good way of doing things. You may think it is discreet, but it is really obvious to anybody familiar with the industry what is going on. That is a major reason why companions get asked to leave hotels on return visits. Additionally, communication in public laws could be an issue.
The most discreet way of having a lady come to you (if she isn't able to get up to your room without any staff interaction) is to simply have her walk up the the front desk and say "Hi, I'm Angela. I'm meeting my friend/colleague/ John Smith in room 1217. The elevator seems to be key carded. Can you please buzz me up.
The front desk will simply call the gentleman, verify it is ok to let you up, and you are good to go. As long as you are dressed appropriately, nobody is going to think twice about it. It also looks much more natural for two people to head to the bar or restaurant together - and it allows the lady to drop off any items she doesn't require for outside time.
The more open and transparent you are, the less you are scrutinized. If you are standing around the lobby, looking nervous, and not sure of who you are searching for, it draws a lot of attention. If you are open and comfortable, it simply looks like any other business meeting.