She's had 13 fits since we saw the Vet on 1st August. The bloods then were clear, meaning there was nothing physically causing the fits. The video helped the Vet confirm, as we already knew, that she was having full Grand Mal seizures.
Because she's now having them about every 3 weeks, the Vet recommended we start her on Phenobarbitone. She's starting on a low dose, twice a day; we need to take her back to the Vet for blood tests in a month to check that it's not causing problems with her liver etc.
It'll take a couple of weeks to have any effect, so she may well have seizures in between. And there may also be some side effects, although the low starting dose will itigate that as much as possible.
Let's see how it goes.