Her impossible claim of 3 month pregnancy at this point is disturbing so she is either some kind of liar or doesn't know much about the reality that you have been away for a year. It is possible that she is mentally ill, but only a professional could diagnose if that is the problem, and what it is.
If you just want to cut ties then block her on your phone and social media.
If you want to help her, perhaps you can tell one of her friends or family to see if they can get her to go to a professional. If a person doesn't want to go, there is nothing anyone else can do to make them though.
So you are saying you have had NO sex with her since December 2016, correct? Verify that as it is important. We have to be careful not to give mixed messages. I, long time ago, had an ex boyfriend stalk me. I was a single female living alone and it scared me. My last conversation with him went like this: I want you to acknowledge what I am saying. I do not want you to contact me at all ever again in any way. Do you understand? (firm voice used) No matter what they say, you say only that. And then you end it, I've said clearly to you that you are not to contact me ever again and am now notifying you that this is recorded and should you contact me again, I'm going to the police to begin proceedings for stalking.
I never got another call, text, email or visit.
But I meant it. I needed it to end. You'll need to say also that you are including your family. Talk to your family and tell them to not respond in any way. Give her no moments to talk, hang up, delete, be done with it.
Apparently, you can get a restraining order for this contact if my research is correct. You can't be "nice" to a stalker. You have to consistently be cold and to the point. Try talking to the police and see if they can put into effect a restraining order for yourself and your family. I read that this could be considered Domestic Violence and you can get a restraining order (in the states) that will effectively stop all communication with you and your family, or she will be charged. It may be the only thing that stops her and allows you to move on. Let us know what you do, or what the police say. Sorry about your predicament.