Well, I gave 7 options in my response of stuff she could do that was not hanging out with other teens, though I do STRONGLY suggest it, but if you are fixated on the spa and only the spa, you perhaps should have researched that beforehand as they will likely not budge on their age restrictions. When I was a kid the only things I remember restrictions on were the spa/fitness center, certain late night shows, adult only pool, adult only sun bathing area, and travelling thru the casino. Literally, nothing I wanted to do anyways.
Everything else I remember being fair game.