Rashi says that the verse uses the phrase “done with her” instead of “done to her” because Mordechai knew Esther was in her current situation for a great reason beyond his own surmise. Mordechai was therefore watching to see how Esther was being used by H-Shem. How is she to be an instrument for something great? To put this in perspective, we all believe Moshiach is coming, but we still want to see how it will come to be.
The Ohel Moshe asks if this is not a contradiction to a previous comment of Rashi’s (on Esther 2:10) where he says that Esther’s revealing her Jewish identity would get her dismissed from the contest. If so, how could Mordechai have expected any good to come from Esther’s being in the king’s harem? The Ohel Moshe answers that one cannot push aside a single Halacha, even to save the Jewish people. He quotes Rav Moshe Feinstein that one must do whatever is within one’s power to avoid a sin, even if one knows that the sin would bring about the rescue of the Jews.