Ivy is pretty humiliated, particularly when Derek instructs Karen to work with Ivy on her voice. Ivy is suuuper bitchy to Karen during said practice sessions, even (especially?) when Karen tries to be nice to her. Ivy warns her not to get ahead of herself, thinking that she's got something Ivy doesn't. After all, MARILYN got help all the time. Girl, you are going to follow this Marilyn role-model stuff right off a cliff, aren't you? "I know what I bring to the party," she says, which I think is a reference to her figure? She then promptly turns on toe and gets all chirpy-girly with the piano guy, which seemed like a much better way for her to illustrate how long Ivy's been playing this game than a hundred "Marilyn did it" speeches.
So the next day, they try a full rehearsal of "Let's Be Bad," and when they freeze-frame it at the end, the whole company (and Ivy especially) have to endure Derek, Tom and the choreographer whisper-conferencing about what they just saw. Again, this feels like a realistic way of getting across the soul-scarring self-consciousness that these performers have to go through. It's all on Ivy's face here, and when Derek is awful about it and tells them to try it again, Ivy keeps false-starting because she's so emotional. She cries in front of everybody but she's also determined to get it right. One more try. You know this one's going to be the good one because the show shifts us into The Musical That Will One Day Be mode. It's the most complete vision of the show yet, and we see that "Let's Be Bad" is basically the My Week with Marilyn number. She shows up late to rehearsals! She's a nightmare to work with! She's popping pills and is often out of it ("Darling, so many pills...")! But oh, is she ever magnetic.
And here's the bottom line: Ivy Lynn KILLS IT in this version. From what we've seen, Marilyn: The Musical appears to be a raggedy thing. There's no cohesion to the songs, a lot of the staging seems overdone, the whole idea of the chorus girls assembling as a demonic horde looking to devour Marilyn whole is a nice metaphor for the Karen/Ivy conflict, but it comes across as hokey. BUT, much like with "Let Me Be Your Star" in the pilot, there are individual parts that are giving you something you'll get nowhere else on TV. That's the case with "Let's Be Bad." Megan Hilty absolutely slays it (she's brassy and magnetic even as she's playing Marilyn's descent into a druggy haze), and even if I think the show is squandering her on a frustratingly written character, I can comfort myself with the fact that she gets to show her stuff on network TV in something like this.