My response is strictly a matter of opinion, and since I have lent my book to someone and am awaiting its return, I cannot point to any lines of text. But it is my opinion that Ruth was completely, utterly unable to disclose her past to her children because in order to carry on, she had to close the door on her past, put a triple lock on it, and not let it appear in her consciousness. Had Ruth thought about her past at all, she would not have accomplished the remarkable feats she did accomplish.
Should she have? That is judgment that is strictly a matter of opinion, too. I cannot imagine having a past so painful that I would keep it a secret from my own children, but then again, my past was not particularly painful. I believe in a considerable amount of openness with one's children. This serves many purposes. It allows children to see that people can transcend their limitations, it allows children to see that their parents are people, and it enables children to develop more empathy than they might otherwise develop.
However, there is ample precedent for concealing one's past, and this is prominent for Ruth's generation in general and Holocaust survivors in particular. Many parents who survived the Holocaust cannot bring themselves to speak about it at all, and I have read of children who did not even know of their parents' backgrounds. My father, who is a World War II veteran, did not even speak of World War II until after I was thirty years old. It was simply too horrible for him to impose upon his children, not exactly a secret, but never spoken of when we were younger.
For Ruth, the past was dead and needed to stay that way. She drew a line between her former life and her new life, and could not afford to go back and forth between them. It is easy to judge her now, but none of us have gone through the life she went through, including her children.