Treat the internet like a firearm and cigarettes. 📱🔫🚬

Children under 16 as a rule shouldn't be online.  They can socialize and educate offline.  With completion of cybersecurity and basic how-computers-and-the-internet-work classes, they can be given gradual access to the internet. 

A child should never "demand".  If you've got a situation where she's comfortable continuing to whine after you said "no" and explained why, then you have way bigger problems than which app to use.  You need to fix that relationship asap or all your helicopter parenting will backfire bigtime.

The sum of the world's knowledge, and a public face to every human on the planet, aren't things you just give to a child.