The first time I did shellac french on myself to test, it chipped fairly quickly. It was all down to not sealing the edges enough with top coat and not making the white super thin. Plus making sure the base coat covers the edges too. I was also not careful enough with them as I had been used to brisa gel & acrylics. I am not an expert but just make sure you really really cap all edges, & sides where the french white ends.
Perhaps do it on yourself as it helped me learn to do french better. You can relax when doing your own and easily examine your technique as you go along. Don't panic, it took me a few applicaptions to iron out a few teething issues, it was all me and not the product. If your doing well with the other colours it will come. Watch fingernail fixer she covers french. Search you will find it on a thread. It also depends how she has looked after them compared to other people, has she used solar oil etc. It may not be you at all.
HTH :wink2: