The girl needs to fit in with surroundings so not to look out of place & that would depend on hotel & other guests
ie
Hidden Image/Members Only this would draw the wrong attention
So Smart Business people in hotel then Skirt & blouse to look like a PA type
If the hotel has a Health club where a lot of locals use means girls in track suites or casual carrying a sports bag won't look out of place & gym goes only stay for an hour or so
If a footie match is on that day a footie shirt of the team ie Utd or City or Visiting team would fit in
Travel lodge more Jeans than Armani suites
who is the room for booking a single room & having guest looks strange, book a double & ask for two keys as other party joining you later when checking in
It is all about fitting into the enviroment & been confident when moving around the hotel reception
One other thing avoid media attracting WGs