The denim shorts about the right length, the wide leather belt....but, alas, she has fair hair. Otherwise Pp would ask her to slip off the shirt, kick off the boots and bend over that fence. A wrist roped to each post would hold her there with more than enough slack to kick up her heels. Later Pp can unbuckle her belt and see how long it takes for the shorts to slip down.
She is lucky the rails are standard guage isn't she? It it were broad guage she would have to ruck that skirt quite a bit higher and lose some modesty to reach both rails.