I was going to suggest a cannestan rinse too.

We've had some ripper nappy rash recently that was so bad it bled and I had to give constant pain relief to change him.
We were using alternatively bactroban ointment (script required) and curash powder. I know power really isn't recommended but we needed something to dry it out and it's the best one I've found to do this.
If the antifungal isn't really working then it's possibly not a fungal thing.
Using 2 fleece liners helper keep him dry too.

I agree with Olive - I doubt she'll even notice the difference between them.
However saying that it can work both ways. We found the plasticness of sposies made it 10times worse.
.... I know how hard it is.