A season 2 episode reveals that Barkhorn calls the dividing line between her orderly half of the room and Hartmann's Trash of the Titans half the Siegfried Line, the name of the real-life defense fortifications along Germany's western border during World War 1.
From the movie. Yoshika is being lectured by Shizuka on the importance of discipline in the military, and thinks that now she understands how Erica felt whenever Barkhorn lectures her. Smash Cut to Erica sneezing.
In the second season episode where Lucchini, Yoshika and Shirley go shopping, Yoshika holds up an impossibly girly dress that Gertrude would want for her sister. Shirley thinks it's for Gertrude herself and instantly has an Imagine Spot about it, only to burst out in uncontrollable laughter.
Also from the Movie; there's a short sequence with Gertrud and some of the others, Trude at first seems unusually reluctant to patrol in a certain sector. But then she hears that Yoshika might be in that sector too; the next we see, she's in her Strikers and carrying a ridiculous amount of military hardware, positively champing at the bit.