It has been a while since mine were 4, but I seem to remember wiping for them at 2, and teaching them to do it themselves over a long period of time. I really think you have set yourself up for disapointment here by expecting her to be a little adult. She's not.
I hate to tell you this (from experience here) they will fail to do a great many things long after you think that they should have picked up on what you told them to do, and if you get too disapointed and upset about it, be prepared to be "crazy" for a long time to come, because they are going to stun you over and over again. Having them not do what you taught them occasionally is just part of parenting, and if you take it in stride and realize that that is typical, you will feel much better about what seems to be a set back.
Just wait. One day you will realize that she has not brused her teeth for a week, or decided she does not need shampoo, or is using the deoderant on the cat...you will be much better off if you just expect the unexpected and learn to laugh at it.
Been there and laughing about it!
M.