Hi guys
I know many people find it difficult to "leave the gap", maybe technically but actually psychologically too!! It feels as if you're not doing the job properly and maybe your clients think you're giving her a half hearted job too!!
One thing to help with the concept of it, is to imagine that, the tiny gap of natural nail could can be buffed to the same high shine as your enhancement (with the softest - grey side, of a 3 way buffer). This way your enhancements will be "seamless" as they grow out. If you don't leave the gap, then your client will see the difference.
Obviously there are other far more important reasons for leaving the free margin, but I have found that giving my students a visual reason for doing it more successful.
Hope this helps