Hi all, no more Pepipoo eh! Glad I found the replacement

Anyway, came home from work to an upset wife today as she's received an 'Notice to Owner' document for a parking fine. First up, just to say she realises she messed up, and is happy (if that's the right word) to pay the fine. However... the issue is, she never saw a PCN on the car. Now, they've included a photograph of evidence that they did place it there on the windscreen. So is it just her word against theirs!? Seems unfair, why wouldn't she pay if the had the PCN. To top it off, she actually works for the council!
Is it worth an appeal or is she unlikely to get anywhere? To reiterate, any appeal would just be to pay the 50% discounted price, not to get out of it completely.
I'm sure she can't be first to be in this situation as I've seen plenty of those bloody PCN documents on the floor before.
Thanks in advance for any advice.
Olly.
PS: Is there a way to get this forum in dark mode? The white hurts my eyes!