"Mind you she also told me off for bending some notes and for using that percussive tongueing technique (which is of course much more common on the low whistle)"

Hmmm... My daughter is a pretty good recorder player. Grade 8 with distinction and all that stuff. She plays a modern piece on recorder - Hans-Martin Linde's "Music for a Bird" - which uses all sorts of techniques I guess your button-holer would disapprove of: overblowing, hard tonguing, squeaks and swoops, using the knee on the bottom of the recorder, and more. It's certainly an established part of the modern recorder repertoire. I can't do YouTube from "work" but try searching on "Hans-Martin Linde Music for a Bird" and you'll find at least a couple of examples. I'd guess they're done well - it's not the sort of piece poor players would even attempt.