One of the three things Moshe added m’da’ato (Shabbos 88) was separating from his wife, leading to Miriam’s complaint which we read at the end of last week’s parsha. It seems from Rashi on chumash (on the words “peh el peh”) that Hashem directly commanded Moshe to separate from his wife. However, Tosfos argues that had that been the case, there would be little for Miriam to complain about. Moshe must have taken the initiative in separating, and afterwards received G-d’s consent (“hiskim Hashem al yado”). Based on R’ Elchanan’s approach (discussed last week) that m’da’ato means the chacham’s intuition of ratzon Hashem, the flaw in Miriam’s complaint is more apparent – the very fact that Moshe took the initiative and had an intuition of some aspect of ratzon Hashem which she did not establishes his superiority as a Navi to her.
What is unclear from the episode is what Miriam hoped to accomplish by voicing her complaint. My wife suggests that she intentionally approached Aharon because Aharon was known as a peacemaker, especially in the realm of shalom bayis. Who better to appreciate the plight of Tziporah and intervene on her behalf?