I agree that wipes might help in the beginning. The extra moisture can be soothing and helps little kids who aren't as dexterous clean away the debris without wiping, and wiping, and wiping (!). Especially if the issue is that she wipes, but it just isn't all coming away, wipes are a decent thing to try. They're also good if she has tactile issues and doesn't like the feel of your toilet paper.
If the issue is technique, maybe make a few (non-graphic)hand-illustrated instruction cards to remind her what to do, go over them with her, and keep them in the bathroom where she can remind herself of how to do it. If the issue is stress over how to do it, this might help. If she likes numbers and counting, have her "count to 5 to make sure you're done", pull off "4 squares of toilet paper" and "wipe 3 times", or whatever.