"She can earn her phone or computer when she publishes an app on the App Store."

I don't understand how building a piece of software that Apple is willing to publish on the App Store makes your daughter emotionally prepared for social media.

I don't have any problem with gatekeeping minors' access to social media (although I would be much more liberal in this area than you) but this metric seems absolutely bonkers to me. My heuristic from my own personal development would be that the earlier I was able to make some commercially viable software the later you should push my access to social media... my coding ability was never an indicator of my defenses against the common ills of social media for kids as I understand them!