DD2 gets extra time for all subjects, including art. Her work is extremely detailed, and meticulous, so I was pleased that she was allowed the extra time.
The thing about needing a portfolio for architecture, is that doing A level art allows you to build that up. Otherwise, you are trying to build up a portfolio, as well as doing A levels, which is a bit of a tall order. She could take a gap year, and apply next year, which would give a bit of time to build up a body of work, I suppose.
I would think universities would want to see a good result for GCSE art, if it has been studied, even if it's not necessary. You might want to check with whoever oversees UCAS and personal statements, etc, at the school.
That's a really crappy teacher, though, allowing her to get to this stage, and then telling her she needs to do more and different pieces. If not already finished, there should just be a few finishing touches to annotation, and so on.