L.D.
This was the situation with my daughter when she was 4 also. Whenever I told her to try to wipe her bottom, she told me that her arms weren't long enough to reach around and it made her feel unstable on the potty. A lot of her friends were the same way. My daughter didn't go to preschool so I never had to worry about who's wiping her bottom (that was me) and she was able to manage this duty by the time she turned 5 and started attending kindergarten. Hopefully you will get some useful advise from some of the other moms here.