The Bechdel Test game: in the original trilogy (Eps. IV-VI), any time two human women are on the screen at the same time, drink. You'll drink once, at the beginning of Empire, when an unnamed Rebel technician appears briefly in the background in one of Leia's scenes.
Twice- the Tonnika Twins are close enough to human to count.
Better still (even though it is a retcon -albeit a longstanding one-), those aren't the actual Tonnika twins in the Cantina scene, but Shada D'ukal and Karoly D'ulin, two human Mistryl Shadow Guards disguised as the Tonnika sisters during an undercover operation...
Princess Leia and Mon Mothma are on screen simultaneously in Return of the Jedi's Rebel briefing scene, bringing the total up to once per movie.