I heard that the problem with Miriam's Lashon Hara about Moshe was that she compared him with other prophets. With this comparation, she downgraded him, as he was a much bigger prophet and even comparing his prophecy level with theirs (Miriam and Aharon) was already an insult.
So, the main point of the Lashon Hara was not that she criticized him for leaving his wife per se, but because, by doing so, she compared his prophecy level with theirs.
Is this correct? If so, does anyone know where this is written?