The big branch looks really healthy compared to the rest of the bush actually. the flowers are big and bright and the bark is still kind of green where the rest of the bush the bark is brownish kinda and the leaves darker, the flowers darker.

You also may want to check how the sun strikes the bush. If the bush is in a partly shaded area, that super branch may be stretching for the sun and even after pruning might continue to do so.

Cynthia

that is something I thought about.
In winter months, it gets direct sunlight from morning til 1pm ish, in the summer months it gets direct sunlight from morning til 3pmish. daylight savings time and the angle of the porch or something I don't know.
I told my grandma I would prune it for her come December or January. I live in Alabama so summer is just getting started here.

Knock Outs do get quite large in warmer zones. It certainly is good news that the branch looks healthy. Would you know if your Grandma prunes it spring. That could help encourage the robust growth to come more uniformly from lower down on the bush. Are the leaves the same shape as the rest of the bush?

No she is too elderly, she has never pruned. Yes, everything is same shape. No suckers coming up from the roots that I can see. :)

Have you ever trimmed the entire bush? Every spring I trim my knockouts to about 18" high. I find that this controls the size of the bush.

Here in fla where advised to trim knockouts once a year to keep them nice, clean and happy. Otherwise they get pretty scary looking left alone. U should post a pic tho of the super growth. It's best to be safe than sorry.