I stayed at Marriots spa at riverside 2 years ago and you will not have a problem bringing the girl. Lobby is big and u can just walk by to your room without any problem. Only problem is hotel is too far from action. You either have to take ferry to BTS or Cab. Most of the taxi driver not willing go to riverside late at night becuase no customer comming back. I would suggesst stay at JW Marriot which is right in the middle of all the action. Don't know about how girl friendly is but I am sure some brother stay there before and can give his feedback on this