I don't know a lot about these plants; I have two that I've managed to keep alive for five or six years but I've never had luck with cuttings because I'm lazy and don't take proper care of them.
I'm curious to know what your clients worries are. She should be able to take cuttings at any time of year but this is the normal time for Holiday Cactus to be budding up in preparation for those beautiful blooms that appear around Thanksgiving and Christmas so if she prunes now she will probably be foregoing blooms on the mother plant this year.