Honestly that plexiglass shield idea is pretty smart for a quick safety fix. I've seen guys use old plastic binder covers or even cut up milk jugs for the same thing. Tbh it's way better than nothing when you're in the middle of a job and can't run to the store. Just make sure whatever you use is thick enough to actually stop a chip.

My last cheap scope made my barrel look abstract art...

Wadesullivan's sarcasm is so thick you could lay carpet over it.

But the craftsmanship alone is still wild!

Yeah when you said it throws off your timing, that's the worst part! Since talking to her directly didn't work, I'd start writing down every time it happens. Like the date, client name, and exactly how she interrupted. Then take that list to the owner or someone above her. It's harder for them to ignore a solid record of the problem.