My sister wants me to root this cutting that was broken off in December; it has been in her garage. Over half beginning to shrivel though. What should be done now?

Betsy;

Now is the Perfect time to plant it in some (slightly moist) well-drained potting mix (like Miracle Grow Cactus Mix)

Just bury the cutting 2-3" below the surface, tie a bamboo stake to it & Do NOT Water until you see a little top growth. Give it a Warm location to root... but Not in full Sun.

They're easy to root, so don't fuss with it... The cuttings shrink/wrinkle when dormant... completely normal

Yes, the timing to start attempting to root is just right. If it were mine, I would put it in a very gritty media mix, container with drain holes, water once thoroughly till you see excess water drain away. Position in a part sun area outdoors and leave it alone...wait, wait, and wait patiently, leave it alone...do something else...

Wait till you see one nice leaf fully open before resuming active watering. Leaf claws do not count, got to have one at least fully open.

Thanks, BBQNBLUES & @tarev.