I feel like when you’re managing a team you also have to consider the skills you want future devs to have to have.

I fully agree.

This particular case is a startup in a very sensitive area rushing to MVP that has chosen to imbue it's devs with a lot of autonomy and build a distributed infrastructure where they treat each other as black boxes. This decision was made before me, not that I necessarily agree or disagree, it's mostly working, but I'm struggling to get everyone to document their shit and I'm concerned about bus factor and replacing people / maintaining these systems in the future.

Anyway, I think that was her thinking when she chose React (wanting to learn it) but her progress has been underwhelming at the last few standups (she's built very little while the rest of the team is rocketing along). She's built so little in the last three weeks that she even agreed (today) that pivoting to Angular makes sense. We'll see if she can catch up.