Okay but going off the details you provided this would've also happened if she were 18+? If not via Discord or Roblox, they'd find some other avenue to groom people, lure them in and kill them. 16 might not be an adult, but at least where I come from it's not exactly a child either.

There's always a chance of horrible shit happening, but we shouldn't put every single person under a microscope to ensure the one in a million doesn't occur.