Yes, it's really pretty easy! I'm pretty sure my girls can manage - dd20 never goes hiking without her tp. Boys need to be taught how to manage without dropping their drawers.If you pull your pants all the way down to your ankles and squat down really low you can pee without it getting on your legs or clothes. I know this from my drunken 20 year old nights.I always carried tissues in my car so we were good on TP.
As for TP, maybe the nannie had a tissue or a wipe? maybe she grabbed it from the car?