I have no idea what is going on. But if you like it, you should take one of the healthy leaves and try to root it. Plus you should isolate it from your other violets in case you have mites or bugs. Sorry I can't be of more help. I'm sure someone else will know what's going on.

Yikes. If you take a leaf cutting make sure to wash it well in an alcohol solution to disinfect it.

Whenever I've had this happen to me, it's either due to too much heat, mealy bugs (this would be my guess of what's going on now), or chloramine in the water.

If you blow on the soil do you see anything very small moving around?

Luckily, I put down leaf cuttings a few months ago. I'm getting some babies now. Yay for paranoia!

I didn't see anything moving. Unless I need to grab a magnifing glass to see them.

It could be too much heat. I'm in Florida, but it was doing fine all through the summer. Now, in the past month, it's started looking horrible. My other AVs in that window are fine.

Fawnee - i would chuck it now, not too many chances to grow it back to normal. And you have babies anyway.
It got exposed to something bad. Doesn't seem like bugs...

i.

That's what I was thinking. It was such a good plant though... Sigh...