Ellen Barkin was indeed in Buckaroo. So was Jamie Lee Curtis.
From JLC’s filmography:
1984 - The Adventures of Buckaroo Banzai Across the 8th Dimension - Sandra Banzai (Buckaroo’s mother) - In extended version only (her scenes were deleted in the version released in theaters)
Ah, never saw the extended.
Did see it in the theater. And the tv version cuts the march at the end.