If he is changing her work she should run word comparisons between her work and his version for a few rounds. And then send these to a senior person, alleging the creation of a toxic unsafe stress cresting work environment. Then do a formal grievance. She’s going anyway.
Long time ago I had a manager who would micromanage like this change words and wording for no reason. I submitted their own corrected text back to them on occasion and they still corrected it. In isolation seems picky only. But when all the changes are written down en mass it's looks like a crazy person. Mine resolved with a lateral move.