My orange rocket barberry has lost most of its leaves. It hasn't grown in the 8 months I've had it. I live in northern Arizona (Prescott). The branches are still green on the inside but all the leaves have dried up and fallen off. I know it's not dead.
Orange Rocket Barberry
Certified GKH Gardening Expert
Adequate watering is important for a new planting.
I would trim away the dead material and increase watering.
I also may recommend a soil test, since you indicate the plant did not grow much.
Here is a link to refresh you on care requirements.