Actually, I think it's doable. Okay, she can't be a pop star on the level of Taylor Swift. But people are going to have different levels of fame in different places. If I say "Justin Bieber and Celine Dion" you probably have a vague idea who I'm talking about, and if they joined Blackwater people would know about it. If, however, I said "Melissa McClelland and Luke Doucet", you're going to be like, "who?"Okay, but...why would a pop star join an elite security company? It's like...if I was running a game set in the modern US, about a bunch of people working for blackwater, and you wanted your character to be a former pop singer who fell on hard times. Culture shock is a perfectly fine angle, but...you can do that without the idea being something that falls apart to even casual introspection.
So, my idea is this, if @Scia is okay with it. I'll admit I never read the William Gibson novel, but the wikipedia suggests an Idoru is manufactured, a Hatsune Miku for the posthuman age. Presumably, Cyrsi was manufactured to be famous and make a ton of money. However, she never gained much fame beyond Venus, or possibly even a cluster of habs there. If you've spent tons of money and effort making an infolife designed to crank out viral megahits and she doesn't do that well and starts whining about "doing it for the art," you might get an idea it's time to pull the plug and start over.
(Note: this also works if she was supposed to be an actor or something)
Obviously Cyrsi wouldn't be agreeable to this, and ran off to a security company. That's the how of how she ended up on the doorstep of the security company, the whys of "why do they keep her around" and "why did she choose this particular security company" are probably best answered in the crossover phase. Maybe someone has a soft spot for AGIs on the team?