As shown by fairly regular posts on imposter syndrome, we can all identify our own failings, so regularly think we don't know enough. We're mostly all seeking progress, so this is a tiny step, for her, based on where she was previously.
Also, re: imposter syndrome and seeking progress, I appreciate Dr Ben Hardy's concept of "Gain vs Gap". We tend to focus on the Gap in front of us (between where we are now and where we want to be), but it's important also to look back at the Gain (relative to where we started). The Gap will always be there, as our goals inevitably evolve, so focusing exclusively on it can be disheartening. The Gain, on the other hand, steadily increases according to our efforts. Using the OP's method of accumulating concrete evidence of increase in the Gain makes good sense to me.
While true, this is exactly the boring conventional wisdom that I tried to steer attention away from with my above comment.
While it’s a blatantly obvious duh-level truism that people can take on larger challenges as they learn, I mean come on… it’s helpful to realize that there remain tiny things — tiny by almost anyone’s definition — even later in a career. I’m not just starting out and just last week I learned yet another way to add in bash, for instance.
You may find it conventional wisdom, but I often find it rare for people to celebrate small achievements. They just wait for the final payoff and don't feel like any intermediate step is 'enough'.