I personally never use anything harsher than a 180 file for reducing length and for de-bulking.
If you are removing any lifting and are close to the natural nail then use a softer 240 grit to do the final stages.
If you are removing lift correctly, your file should rarely ever get too close to the natural nail.
I have witten several tutorials that are here on the site, in the tutorials section under nail maintenance. I believe the title of the one that would help you is 'file control part 4 .. During the re-balance.
Good luck, this is one of the most important aspects of what we do and keeping nails healthy and undamaged should be the top priority in your mind along with preventing any problems for the client over the next few weeks of wear.