Great Dragons have clear power. CEOs have clear power. Frosty has clear power (and lots of it). But those are all quantifiable things. Great Dragons have power not only because of their species, and their size, and their strength, and their magical talent, and their knowledge (being a "Great" takes time and stuff), but also because they travel in certain social circles and wield immense worldly power, while rubbing scaly elbows with others who do the same. Heck, even your "Barrens brat vs. high society princess" example has all sorts of built-in contacts and assumptions about financial resources and stuff (all of which is clearly quantifiable through the rules that govern those very things, with contact ratings and the resources portion of chargen). Same thing with a CEO, that's all about resources, and contacts, and stuff. Right? They're descriptors, and they describe someone's worldly power and status, as much as they do anything else. When you call someone a Megacorp CEO or a Great Dragon, incredible amounts of power are inherent in that descriptor.
Here's the disconnect, though -- none of that sort of power is actually inherent to being an immortal elf. This is where Frosty comes in. She doesn't have her power and influence because she's an IE, she has her power and influence because she was Harlequin's apprentice for years and years, she inherited a power focus from Dunkelzahn, she's been an active shadowrunner for decades, and because she's built up a social network (on Jackpoint, for instance, and among those other ageless movers and shakers) that matches those experiences.
When she was just an unknown bastard brat growing up in orphanages and foster homes in Missouri, and putting herself through school? The fact she was immune to aging wasn't that big a deal. So what's the harm in letting someone play Frosty as of twenty years ago? Leave it up to the player and the GM to see how much, or even if, she ever gets pulled into Ehran's troubles, under Harlequin's figurative and Dunkelzahn's literal wing, etc, etc?
I'm not saying "let someone play Harlequin." I'm saying "if you brag about your First World survivor GMPC in the same breath you say you'd never ever let a player be immortal, it's a red light to me." Heck, if anything, I'd think in a campaign full of First World survivors and intricate Immortal Elf power-plays, it would be even easier to insert some sort of powerless schmuck Frosty-as-a-college-kid type of character, thrust into the middle of that campaign as a catspaw without really knowing why.
