Penemue never fell. It was all a giant misunderstanding.
She loves humanity. There’s nothing wrong with love. It’s one of God’s guiding principles. Even the angels still in heaven will tell you that. So maybe she taught the mortals she cared for a bit more about medicinal compounds than Jean and Novalis though was appropriate.
And maybe as a young Elohite she spent some evenings in the bed of her most promising students rather than keeping an eye on the Grigori as she was charged. These things happen when you truly love the divinity of man over the divinity of heaven. But Dominic declared she could not return to heaven and the other Archangels backed him, and so she has not returned.