Thanks Grace, I appreciate your and everyone else's time and thoughts.
Not quite sure what you mean by more 'telling her so', I don't understand what you're suggesting I tell her?
It is interesting reading everyone's perspectives and experiences. (quiddity - that sounds dreadful, sympathies 
)
I guess one thing, if you don't mind the honesty, that has kept me off the thread before is that I'm not against firm labels and feel that there is a sliding scale of narcissism - I am of the opinion that there are some people who are very narcissistic but who don't have NPD and who are able to modify and recognise some of their bad behaviour.
I don't feel that my mother is black and white at all, I recognised an awful lot of her on the daughters of narcissistc mothers site - in fact, that was a revelation. But I try to be fair in all things, and so I have to say that she can be caring and selfless and empathetic. One of the big problems of my childhood actually was my mother's Jekyll and Hyde persona - one minute I was her pretty little girl, the next I was her fat pig. There was no consistency or middle ground really: she was either very loving or very hateful. And obviously this is abusive, because the bad was bad (so much so that I had a therapist in tears once 
) But even now I find myself reluctant to lump her in with everyone else's narcissistic mothers and say she's completely toxic, because she isn't completely toxic.
But then, the main reason she has changed dramatically in the way she deals with me is because I made her. She wants to see my kids, and she knows that means no funny business. It seems ridiculous having to spell out to a middle-aged woman that you won't see her any more if she carries on going on about how fat and disgusting you are (when clinically you are only half a stone overweight), but that's what I had to do in my mid-twenties. And then before I let her meet DD, I spelt out that she was to treat me with respect.
I think one thing I've gradually come to realise over the past few years is that it's my father who is the true, and absolute narcissist. And that, although I'm loathe to admit it, he has dominated my mother far too much and is probably emotionally abusive to her because of this.
He is the one I have gone NC with - there is no rationalising with him, no negotiation, no way he will 'tow the line' even for a few hours for the sake of other family members. Seeing my children - who he does really love and enjoys playing with the seven or so times he's met them - is not an incentive for him in the same way it is for my mother.
So, seeing my mother without the father, and with me with my new in control attitude, has been a bit of a revelation. I am the one with the power and the control and she knows it.
I suppose that is what I feel guilty about. Not telling her I'm going away when she is trying (reasonably) to arrange a time to visit is game-playing. And although I don't necessarily owe it to her to treat her with respect, I do feel I owe it to myself and to my children to model respectful behaviour. I should really tell her we're going. I just can't stand the thought of all her interest, all her wanting to to talk about it (again, quite reasonably - we are after all going to be visiting a country she used to live in). I just hate sharing anything with her. Not because she uses it against me or is controlling, I know she won't do this any more, but precisely because she has done this in the past and so for me, she's had her three strikes and she's out. I don't tell her any of my career successes or about my friends who she knows or anything. I have told her about other holidays but this one is special for several reasons and feels to intimate to share with her.
But then I think, well when anyone else asks me about plans for next week or so, I would of course tell them I can't because I'm going away, so shouldn't I behave in the same way towards my mother?
I guess this comes down to acting like an emotional teenager versus acting like a mature, rational woman. I don't know which to go with! Am I doing myself a disservice if I game play? Hmm.
Sorry, another long post. But it is good to have a place to thrash all this out with people who understand 