They are giving out their phone number to people they met on roblox.
The child is institutionalised, their parent cannot control their behavior meaningfully and the adults at the institution are pretty negligent and she doesn't trust them.
I have messaged like my whole family and some friends for advice but nobody is getting back to me.

What a bind this is, to put it mildly. That might actually be worse outcome than accepting exposure to online predators.