Without knowing which database engine (MySQL comes with more than one) she was using, nor the testing that she actually performed, what makes you say that?

I remember versions of mysql whose string indexing was sufficiently limited on every available backend that this would've been the correct change.

Hell, back in ... 2001? I think? I ended up making exactly the same set of changes to an early database design of mine, for pretty much the same stated reasons and with very similarly pleasant effects on its performance.

imo “clueful”/clueless is more about being able to sense situations where there is something to be known rather than knowing everything upfront all the time (which is obviously impossible)