it depends how vicious she'll be when she realises you're blocking her.
If you want to do it the quietest way, develop a sudden case of Dizzyness.
Start forgetting to answer her. Or answer some of the time after 2, 3, 4, 10 days. Say sorry when you do "I forgot". Start being out when she calls, if she does, or just about to go out. Make vague arrangements "oh yes, we'll have to arrange that sometimes" and never do. "sorry, can't make that time". Never tell her anything important or your plans. Be vague as you can. Deliberately make mistakes about timing - turn up half an hour after you've arranged to meet, if you can't get out of it.
If you really want NC let her call you names. Laugh and brush them off "yeah, I'm dozy" as though it's endearing for you to be scatty. Dozy with a rhinoceros hide!
She'll pin you down at first but as time goes on, being as evasive as fog will make it harder. Hopefully she'll get annoyed and find pinning you down too unrewarding.
Suddenly going quiet on her might actually draw her attention.
If Dozy will work, then that's not bad. If it won't work, then it would have to be more overt; distancing yourself by not answering. Will you have to see her at family stuff though? A formal NC can make that harder though it's sometimes the only way.