I thought I'd add my 2 cents, having both visited girls at hotels and booked hotels specifically to "entertain". Problems I've encountered when in visiting mode:-
Premier Inn and Travelodge are great. Some are acquisitions from other chains (e.g., Holiday Inn), so the keycard system may differ from one establishment to another. I make a rule that if the girl cannot be arsed to take the trouble to fully understand both sides of things then she is not worth a visit. Her ability to book rooms in future if she were to have an imaginary board outside her room which says "please queue here" should be as compelling to her as your possible branding as an opportunist thief is to you. Sounds mercenary but this is a good way of weeding out a good punt from a bad punt.
Other hotels can be problematic as they may ask "who are you visiting?" The small "guest house" type hotels can be like this. The girl should volunteer this information. If in doubt: ask her. If still in doubt say you cannot find the place and get her to come out and meet you at a nearby location. If she won't do this then it will probably be a bad punt anyway.
A lot of girls now work from Serviced Apartments. Some have someone on the door and some don't. If you are uneasy then be very firm about asking the girl how to get past reception. If she doesn't inspire confidence don't go in. Singling out two well-known places in South Kensington: they have hundreds of tenants, many of whom are short-stay, just whizz past Reception and use the lifts. If even this troubles you for these two places then be busy listening to your mobile answerphone messages as you enter the building.
Plan B: You've saved yourself £££ for another day!
The scenario that most bothers me, that is probably at the back of your mind too is that you are on cctv when wandering around trying to find her room. If she doesn't let you in and you have to walk out and there are reports of a stalker or opportunistic thief in the area. Then what? This is the reason to explain to the girl if she doesn't understand your reticence about going directly up to her room, if she doesn't understand this then she is not worth a punt (Irish or otherwise). HTH