Duolingo was exceptionally useful to get me started on my language learning journey (Spanish, a bit of Japanese) while knowing basically nothing. It tapered off pretty fast, is very slow to introduce new vocabulary, and the core lesson structure doesn't explain much unless you dig into the submenus with intent.

As a basic starter tool, it's cute and briefly enjoyable, and that's enough. But you'll need to supplement it with something else almost right away, and your daughter's structured classes and reading material were almost certainly that something else. I think Duolingo's *streak* is the only key feature worth imitating in any form, as it gamifies habit development, which is difficult for many people. If only the lesson content could keep up with that one good idea.