Possibly…
A Grande Dame would display horns pointing down to hell. So this 2018 Oscar appearance, with those earrings, might (I say MIGHT) be a Grande Dame displaying signs.
However we would need to see more blatant displays to really accept this idea
In 2012 she wore a gold dress at the Oscars. Also earrings that are down pointing horns but the only other rank symbol I can possibly see are the 5 rings on the belt, which would make her a witch down at the 5th circle of hell. Not sure if this is enough to be a Grande Dame, but perhaps all the witches from rank 1 through 9 might be considered Grande Dames.
Anyone have more info?