I think the most important part is - "but the bigger benefit is you know how the entire system is architected and the code you’ve written impacts millions of people".

Seriously, you feel empowered when you know why the system is architected this way and not that way. Its immense satisfaction when you can see through how the entire flow works, how a new feature fits into the bigger product vision, how to debug complex issues by traversing through bunch of different code hierarchies/directories, etc.

You get this kind of wisdom only when you're in the those first few.

On the side note, it would be great to hear first-hand stories from her about how she got hired, how much salary + equity (in approx. range) she received, how was the performance rewards system for an early engineer.