She was a 15min walk away, and you text her with 12min to go. Given that you will not normally get an instant reply from any girl, do you have a tardis?
She could have still been with the previous client, or freshening up after same. FFS you are not the only one she will be seeing on any given day. A wee bit of consideration will make your punting life a lot easier, cause if you don't, you won't have one.