The shrub itself is a little awkward looking, but if it’s grown well it can be a nice addition to an informal garden or woodland. The flowers and the fruits are quite interesting, and the shrub itself can be shaped by pruning if necessary. Never trim or shear mahonia from the top — instead, identify the individual stems that are too tall, too gangly, or growing out an angle, and then lop them off near the ground.

Mahonia does self-sow as the birds eat its fruits and deposit the seeds on the ground. It could be your sister is surrounded by mahonia “volunteers” where she doesn’t want them, and this is what causes you to refer to mahonia as “terrible.” It is easy to remove these shrublets when they are tiny, the same way we have to do with pine and holly in the South. Also, you and your sister may better appreciate one of the new hybridized cultivars of mahonia, like ‘Winter Sun’ — it reportedly blooms earlier (late fall) and has larger flowers in a brighter yellow.

Mahonia is a good choice. I’ve long thought about growing one, or more ever since I saw one in the snow in front of the Seattle airport.