It really doesn't matter. Just use the max "yellow" for soft and the max magenta for "hard". In split grade printing the "actual" grades become a bit meaningless.
There are 2 "modern" subtractive color standards, Kodak and Durst. The major difference is the size of the density steps. If she really wants to know what max contrast ranges she is approximating, just research the standard used by the head. Most heads will give 00-0 soft, but only 4-4.5 hard. But again, the split grade concept makes this rather academic.
Cheers,
Geary