I love this story, thanks for sharing and I’m so excited for your daughter!! I was WashU '14 and loved my experience there, made wonderful friends and connections that have always boosted me in my career.
One special thing I want to call out about WashU grads is that many of us chose this school because it had a reputation for being inter-disciplinary and collaborative and having a service-oriented mindset. Unsurprisingly, students who self-selected for those values also tend to be guided by them as they launch a career. Sure, there are definitely some really smart and ambitious students there who climb the corporate ladders (and serve on nonprofit boards), but at least among my circles, WashU students tended to think really critically about how they wanted to use their skill set and passions to serve others and address critical problems – whether through STEM, business, arts, medicine, law, etc.
I think it’s just invaluable to spend four years in a place that actively encourages you to develop your own vision for what you want to do with your career – before you enter a corporatized world eager to gobble up agile young minds and turn them into profit machines. Several of my friends have left high-earning jobs to take on work they felt was more meaningful – from Big Law to federal government, corporate marketing to a climate tech start-up, blending engineering with public health, picking OBGYN or pediatrics instead of orthopedics, etc. I hope all colleges have that sort of culture, but from my experience, I can tell you that WashU definitely does.
As for WashU being a ‘secret,’ your story is very similar to mine – it’s not a secret among high school admissions counselors or hiring managers in basically any field anywhere in the US, but because the school’s star only really started to shine nationally in the last 20ish years, it’s unfamiliar to a generation of parents not from the Midwest (including mine).
When my guidance counselor recommended I apply to WashU senior year, I looked it up in my big Fisk book and thought “This sounds like just what I want, why haven’t I heard of it until now?!” Well, it’s because I was the oldest child growing up in CA in the 2000’s with parents who didn’t talk to other parents about colleges (and also because I read the book in alphabetical order and hadn’t quite hit the W’s yet 
). But that didn’t matter, because my college counselor was well-informed and pointed me in the right direction!
When I got to WashU I met tons of kids from CA, NYC, Chicago, DC, Boston, Texas, Miami, and tons of mid-size cities (and rural areas too), so I’m pretty sure the guidance counselors there know about it too, and then those alums go spread the word everywhere when they get accepted to great grad schools or hired at top companies. The secret is out!!