Which is precisely why the Constitution explictly gives the Congress ultimate dominion over the seat of the Federal Government: a federal city thats only under local control can do things that make the Federal Government miserable, either as a form of retaliation or blackmail.
I’m guessing the new DC mayor is bluffing to keep the Liberal millenials in the increasingly gentrified DC from turning on her. A suit would be a complete waste of time, resources and money given the explicit relationship, as spelled out in the Constitution, between the Congress and the District (plus 200+ years of precedentvand case law!)
Keep the Liberal millenials under control is the game.