Which is the greater good? The good for all, or the good for a few?

Suppose you have news to report, but it is the worst possible news that ever could be.
So bad that you are inclined to say nothing. After all, the catastrophe is already well under way, and cannot be stopped; its effect on people is irreversible, and those already affected do not seem to realize what has happened to them, or not until long afterward.
So why not leave them in the bliss of their ignorance?

On the other hand you also know that it is possible for a few people, a woman and her children, to escape the general fate, but only if she is willing to make an extraordinary self-sacrifice. Such a woman would also be extremely determined, strong-willed, and above all, devout (not in the religious sense, but a person who, once having decide that a given thing is essential, will do anything necessary to realize it).

How does one locate such a woman, without divulging the details of the catastrophe? This is necessary because a general awareness of these details would destroy the available escape.
N.B. You should assume that the end result of the completed catastrophe is the extinction of the human species.