The first issue here is that she never registered her original work with any copyright registry. It's $55 for 750 photos for the US Copyright Office, which is more or less accepted worldwide. (Also, she's living in the US and working there.)
That leads to the second issue which is that it is now impossible to determine if the painting is a derived work off her photo, or if it is a derived work off one of the countless other images on the web that look pretty similar. (She can't argue that the artist should have know her photo because it wasn't registered)
Together, she's relying on implied copyright (because she didn't register) and arguing that she's famous, so it has to be her photo.
And to that, the judge replied that the photo is not unique enough to make that "it has to be my photo because I'm famous" argument work.
Do the images look similar, like it's the same person? Yes, but that's likeness rights, which the photographer can't sue for. The photographer can only sue for unique aspects in the composition and I'd agree that it is a pretty generic model shoot with pretty generic decoration and a pretty generic pose.
The women depicted in the photo could probably sue and win. But she didn't. This is only the photographer suing.
More info: https://www.tageblatt.lu/headlines/affaire-dieschburg-zhang-...