I've read that the most a rooting hormone can do is to give a cutting that was taken at the "wrong" time or the "wrong" part of the plant almost as good a chance as a cutting taken at the "right" time and place.
That author was clearly dedicated to propagation! Many of his suggestions were like:
"In Year One, do these things to the plant: .....
In Year Two, do this: .....
In Year Three, take cuttings from THIS part ... and plant them like so ..."
He seemed to think that rooting hormones were cheating, or at least not necessary if you devoted your entire life to knowing each species and producing plants with young shoots that are eager as heck to put out roots.
Personally, I think the hormones might not be needed BY your sister or this author, but maybe ARE needed by an amateur like me.
