Suzie says

I’d block her outright – on social media, phone, everything. Tell your family you don’t want anything to do with her and make it clear that you’re not going to justify or explain why. You don’t owe her anything and you don’t owe them an explanation either. I suspect they’d understand, anyway. Bullies don’t confine their behaviour to one person and your example may give them the strength to do the same. But if it would help you feel better, you could message her what you’re doing and why and say you no longer want any contact with her.