If a Batgirl movie is looking to be one of the next movies to actually happen we could get a casting announcement soon.
Beyond this year’s Aquaman and next year’s Shazam and Wonder Woman 2 no other DC film’s have set release dates.
Everything else exists in this nebulous cloud where the movies have been announced, but are otherwise mostly just waiting around.
At this point, we have no idea if anybody is being seriously considered for the Batgirl role as we have no idea what the status is of that movie’s production.