Excuse me for trying to help! For someone who knows Prague it may seem obvious but some hotels don't allow escorts for sure! Hotel Tulip is one for example.
I was just giving people a list of hotels they can feel comfortable at.
Jack is right, some of them want a girl's passport if she comes to visit and is not a registered guest. Best is to use a larger hotel, and meet her in the bar anyway. Just FYI, Budapest and Kiev you also have to be either very discrete or pay a few euro to the doorman to look the other way.
The Marriotte, Hilton, Savic, and Carlo IV Boscolo in old town Prague are NOT escort friendly! (personal experience). The first three have elevators that require room key access, so you have to meet the lady at the bar or outside and take her up to the room past the valet and hotel security, while the Carlo IV you go up the long stairs and come face to face with the reservations personell that are staring at your face.
The best escort friendly hotels are Grand Praha hotel on the square(ask for a room in the next building)because it resembles an apartment, Ventana Hotel (it is advertized as a romatic getaway, and the reception does not care) and the Clarion in Old Town. It is a cheaper hotel but the suites are very impressive.