Looking at just the first few newspaper articles and surveys was enough to conclude that the media agenda influences the public agenda. After that, it was just a question of watching the evidence pile up.
It seems like she went into this without a hypothesis, a (relatively) superficial look at the paintings let her form that hypothesis, and further, more in depth looks at the paintings only confirmed and didn’t contradict that hypothesis.
That seems like the normal and appropriate process for discovering things like this.
Yes, confirmation bias is a problem, but it always is. That’s just how humans work. The mere existence of confirmation bias (which makes it plausible that confirmation bias was at work here) doesn’t immediately discredit the results.
I’m trying to say that confirmation bias might well be a problem here (though the presented evidence seems strong and I personally can’t think of good alternative explanations for what she found – but I’m also not an art researcher) but that is nearly always the case (when it comes to squishy things like this, I’m not necessarily talking about physics, but it’s certainly also a possibility there). So yeah, you can write “Confirmation bias anyone?” under a great number of scientific papers, but that alone is not very valuable and constructive.
Sometimes the process of discovery itself just cannot be sufficiently protected from confirmation bias (in the sense of excluding any chance of confirmation bias), especially when it comes to something like looking at a painting and trying to figure out its history. Then you have to just roll with it while also being aware that it’s a huge problem (preferably by going through your evidence with a fine tooth comb, always looking for alternative explanations – better yet, you should get many other people to do that, and I bet they will in this case).