Objectivism can only be factual statistics. In the case of helping the woman, you did actually objective help her because it can be cited from evidence via the witness and receiver of the help, and thus becomes a fact, but the means to reach this objective state was entirely subjective, as you chose to follow your super-ego with its subjective reasoning of morality rather than succumb to the id and its subjective reasoning of momentary pleasure.
Advanced concepts of good and bad arise out of the super-ego, which is not always present in some animal species and some humans. In the case of the animal, good and bad is a manifestation of pleasure vs pain rather than morality vs amorality, which both pairings are still subjective. An interesting example would be a person with Self-Defeating Personality Disorder and Sadistic Personality Disorder, which causes biochemical pleasure when the person fails/hurts something (respectively). If good and bad were completely objective, then these two disorders wouldn't exist (as the sadist sees doing bad as good/pleasurable since it causes pleasure, and the masochist sees failing as pleasurable, and society sees failure as bad and doing bad as bad).