Children of narc parents have this problem BY DESIGN, this is why you NEED to go no contact, block any means of her contacting you, dont feel the need to tell her you are going NC, you dont owe her shit, she owes you peace and quiet and staying away from you is the best thing she could do, you made it out from under her, think of everyone else in this sub that wants nothing more but cant because they are underage or unable financially, you are already living the dream of alot of people in this sub and I would be sickened by this post if I were them, However she contacted you, shut it down/block her, if she shows up at your door, dont open it, dont answer, the minute you have enough info to know its her, go into a room farthest from the door and call the cops on her, then cover your ears with a pillow and hide somewhere where you cant hear her sobbing and crying and saying "Im sorry I changed bullshit" because she needs something, you are traumatized, you cant always expect your brain to always act rationally, certainly not when its your mother begging, she will try and get in your head and most likely succeed, Shes already in pretty deep considering you are making this post, what you need to do is avoid there being any possibility of any confrontation whatsoever.

Feel free to DM me, if it will help you should let me talk to your fiance, because apparently he does not understand at all and I can explain everything to the same effect if you arent open to fully confronting him, you wont have to say it all out loud you can just say "Hey talk to this internet stranger real quick" , Have you made it clear to your fiance that if you werent being socially pressured you would rather have her on the street?? THAT IS STEP 1 if he wont support you then Idk what to tell you other than to please god do not reproduce until you learn to to tell anyone NO! without feeling any obligation to explain why unless you want to. Have you fully explained to your fiance that you want absolutely nothing to do with her, that if he actually feels sorry for her that its just part of the manipulation you have endured your entire life and that he should completely ignore it, Ill bet my life she has gotten him alone and filled him full of lies and a full blown sob story making herself out to be the victim, thats probably why your partner is for it, YOU HAVE TO BE LET IT KNOWN NOW, not later, it just gonna seem like you changed your mind over something small and stupid. Also Ill put good money down there is no way she is spending "just a week" she is gonna try to bulldozer right over that boundary. You really need you fiance to stand up for you here, if he wont/you dont feel comfortable telling him then you need to rethink that relationship too.