Won't clean

My cat won't clean her butt. Well if she does do it she doesn't do a very good job. I just took a piece of papertowel with warm water... no soap and washed it for her. Then she started licking it.

Is that good enough or is there something else I should use?

Sometimes this is an obese issue, and the cat cannot reach herself to clean.

Oh she can reach. She's only 10lbs. After I cleaned it she decided to do it herself.