Fill-Lines & Shadows:
Note 1: Lifting can cause fill-line shadows.  After you eliminate lifting, you will have fewer problems with fill-line shadows. 

Note 2: Another cause for fill-line shadows is over-filing the pink, to get rid of the fill-line.  This over-filing can cause the natural fingernail to heat up from the friction; which can then cause the acrylic, ever-so-slightly, to lift while you are still filing; which makes it seem that you will never be able to file the acrylic smooth to the natural fingernail; as the acrylic continues to lift, ever so slightly.

Note 2a: The way to counter-act this occurrence is to apply a small dab of primer on the acrylic to soften it; then file (using the Tammy Taylor 'Long-Lasting Zebra' 180-grit file); this allows you to file the acrylic lightly to gently smooth the acrylic to the natural fingernail, and without friction; as friction causes heat, and further lifting.

Solution: The Client can use the Tammy Taylor "Nail Maintenance" kit, to help keep their acrylic nails from lifting in between fills, every 2 weeks.

Below are 2 PDF files you may print, to see a step-by-step procedure and products to use for nail "Maintenance" for both "acrylic" nails and for "natural" fingernails.

Nail Maintenance for "acrylic" nails
Nail Maintenance for "natural" nails