I, too, struggle constantly with Marnie. She's this weird blend of little girl desperate for attention and sociopath, and sometimes it's so uncomfortable to watch her that I have a visceral response when she's onscreen. But that YouTube video? Completely amazing. Probably the best thing I've seen all week.
And I'm with you on seeing more of Adam's sister (Gaby Hoffman killed it in this episode), but not too much. It's one of those things where I don't want her to overwhelm the narrative.
Did anyone else notice that Jessa was in the episode but never even had one line?