Primrose runs her own accountancy firm and attends a workshop on changes to the not-for- profit registration system. She has recently had two knee replacements and this is her first day back at work. Unfortunately, the tiered seating for the audience has been negligently constructed and collapses part way through the seminar. Other audience members suffer minor bumps and bruises, but Primrose suffers major injury because of her pre-existing condition. Primrose's knee replacements have to be redone at great expense, with great pain and the need for extensive rehabilitation and further time away from her business. The defendant to her negligence action denies that they are responsible for this extra damage as it was not reasonably foreseeable by them.

Is the defendant responsible for the extent of Primrose's damage? Give reasons for your answer.