That seems to be pretty clear to me.
It's hard for me to read this is as anything other than "I am not talking about this because I want to change the mind of my colleagues in physics [because they're too far gone]." That is, she believes the research is worthless and the problem shouldn't be investigated. She just doesn't think she can convince people of this.
This is just one interesting sub-problem in physics and if you choose for a career in theoretical physics you know that not everything that you set out to do you will achieve and I suspect that in this particular case it is a let down of fairly large proportions.
So you get a lot of internal struggle to justify the choice, the sunk cost issue is massive and your colleagues are going to go and continue without you. All that needs to be justified to the 'self', both on the off chance that they will come up with a solution when you gave up as well as about all of the time that you now feel that you have wasted.
And in the realm of self justification 'I will stop working on this problem because I no longer feel like working on it' is a lot harder to sell to the ego than 'I will stop working on this problem because I feel that it can't be solved in a meaningful way'.
I'm fine with it, either way, I've seen enough people struggle with career choices made in their 20's when they were in their 40's not to recognize the symptoms: you have reached the halfway mark in your life, what do you have to show for it? And if the answer is 'not much' then that can be a problem. But it doesn't have any value for others, that's all just window dressing and ego-placating.