Queenme, I was just like you. I just thought the JWs were another garden-variety Christian group, didn't really know what cult meant besides legalistic. I have been thoroughly disabused of that notion. The things I have learned...
I don't know how much you want to save the friendship. You're in different countries and if these are your only interactions, there's not much there besides childhood nostalgia. People grow apart; you don't have to stay friends with someone who clearly doesn't respect your previous requests to stop the preaching. If you're ambivalent about the friendship or if you still care about her but don't care if she talks to you anymore, ask her a few questions she can't answer or will have very embarrassing answers. Hadriel gave some good ideas. Or tell her you know she's counting time and share some of the "bad news" about the JWs. There's much to choose from--child abuse, false prophecy, hypocrisy; out and out lying; unscriptural doctrines, etc. With conversations like this, making a placement won't be worth it to her. Be firm but gentle and genuine; she might need you later as a true friend.