Hmmm. The rash was doing really well. It had cleared up entirely in her armpits and she just had the residual scabs from the sores on her tummy. The medicated shampoo works really well; I'm using it once a week on her undercarriage. Luckily she seems to enjoy this, which is just as well because I have to shampoo her twice. the first time it gets washed off immediately, then I shampoo again and leave it for ten minutes before rinsing.
So she's on a restricted diet (no chicken or beef) and weekly shampooing, no more tablets. I thought we were making great strides until a few days ago when, wham, it all flared up again, worse than it's been in ages. There have been no environmental changes this week. The only thing I can attribute it to is that a) I mistakenly gave her a small piece of the wrong hotdog that contains chicken and b) I made a new batch of fish stew and used lentils which I hadn't in the two previous batches.
Now, I'm not inclined to believe it's the chicken because the piece of hotdog was very small, and anyway she snaffled four whole chicken breasts a couple of weeks ago with no effect.
Could it be the lentils? I mean, it would make sense - I started using lentils in their home-cooked food around the same time as the rash started.
It seems weird to me, but it's a running hypothesis. I've binned that batch of food and have made fresh without the lentils. I just want to get back to no rash at all.