Ok Spy, first of all, N's tend to write nice letters in order to reel you back in as a supply source. They don't play fair and they aren't interested in cultivating a nice, loving relationship with you either.
Second of all, if you absolutely cannot stop yourself from wanting to talk with N "mother" here are a couple of suggestions:
1.) Record the convo. That's right! Get out a little tape recorder and record your entire convo with her. After the phone call, write down a quick journal of what happened, how you felt, what your next actions will be, and any other thoughts. Listen to the tape of the convo, and really HEAR her voice, intonation, and notice how you respond or react to her. Use this as a case study for yourself and maybe even to play for yourself next time she tries to lure you.
2.) Have a trusted friend listen in on the convo on another line or on a 3-way convo. I used this technique once to trap a former BPD friend. A mutual friend of ours told me that BPD was bad mouthing me for a long time to her, just like BPD would do her to me. Not wanting to believe it to be true, I decided one day, to have the mutual friend 3-way with me on the line (silently). After I heard for myself, BPD ripping me to shreds behind my back, I then picked up the phone, called BPD, and proceeded to confront her word for word with what she said. Needless to say, she didn't have much to respond with...she had been CAUGHT RED HANDED!
Just some ideas.
Be careful.
~Laura