if her hair is fine, you can actually get a nice grey blending with an
opaque demi. Like wella color touch or Richesse.(loreal). if its thicker, and
she wants 100% coverage, 20 vol is the only way to go. I like to go a level
lighter around her hairline, to avoid a dark band. Also, add a cool tone to half
of your natural to avoid too much warmth.