Maintain YOUR boundaries. Your first duty is to yourself, not someone from decades back in your past.
a. Ask her to stop. Politely, clearly, simply.
b. If that doesn't work, Unfriend her. If she gets all stalkerish, tell her to stop. If she doesn't, call cops. But it probably won't come to that.
c. Invoke "The Woodchuck Solution". Save that as a last resort.
