I have heard these accusations from both sides for many years. No one of either viewpoint has ever said anything than vague, veiled hints at "could have done more". To me it sounds like just another [royal] family feud.
In my own opinion, I think it stems from the sisters supporting their brother [Carol II] over their nephew [Michael].
Let's face it, none of them came out winners under the communists, so I find it hard to believe that had anything to do with their "hurt feelings".
There is even a feud going on today, within the family, but that is another issue.
Cheers,
Robert