I suggest you arrange a Skype/FaceTime meet and greet with the parents and kids first so you can verify it’s a tween/teen girl. I’d tell my DS that most parents wouldn’t be comfortable with their kid meeting someone they met online so to make the girl and her family feel more comfortable a meeting Skype/FaceTime first is necessary

This is not a friend of a friend or anyone I know at all. I don't see an actual meet up any time soon since she lives several hours away, but if we did, it would absolutely be in a public place with us present.

I think it is time to meet in real life to make sure she's an actual 12 year old girl. Public place with you elsewhere in the same place (like a coffee shop).

Unless this is a friend of a friend where someone you know in person can vouch for her, I would not let them talk outside of the game.

DS is 12 years old and plays Fortnite with a lot of friends from school and has also become "friends" with people he doesn't know. There is a friend who gave him her phone number and they talk about meeting in real life. She lives a couple of hours away, so I don't see them actually meeting any time soon, but is there any issue with letting them talk on the phone (they already "chat" in the game)? Skype?