I realise I also forgot to ask the obvious question: can anyone suggest
the name of the likely culprit. She's also wondering whether pruning the
affected shoots well down the plant and offering them to her chickens
will be sufficient to control the thing.

They are in fact called the phygelius weevil or figwort weevil. Cutting off
the affected areas and giving the rest of the plant a blast with some
general garden bug spray should do the trick. I had a few on mine but
picking off and squashing the adults and spraying the plant got rid of them.
Can't comment on their palatability to chickens though