I'd just like to say how interesting and helpful i'm finding this thread. Thank you OP and thank you everyone who's contributing.
My mother has always made caustic and manipulative comments which have hurt me and now she is in her 70's and her social graces are really crumbling it can sometimes feel like having a conversation with a steamroller. She just ploughs on and on with what she wants to say regardless of anything.
I have 3 DDs who, although they love their Nan, are in their teens and are old enough to howl with laughter at some of what she comes out with (once we are back home) which has helped alot in fact. It's made me see that its her thats in the wrong/not normal, not me.
From this thread i've recognised a few things she's been doing for years:
-The need to keep bringing up things she's done for me, financialy or otherwise. As if i've not been grateful enough.
-Snide remarks about me being fat (i'm not over weight, but have to watch what i eat to keep it that way). Only the other day she was telling my youngest about how the vet had said her cat was fat and warned her about it overeating. Mum said to my DD "Your mum would know about that" 
-The tendancy to become suddenly ill everytime we have a holiday abroad, or during personal crisis' like my miscariage.
-The tendancy to totally ignore any change i try to make to myself like hair colour or weight loss. I've gone from blonde to brunette overnight in the past and she hasnt commented. About 5 years ago i lost 3 stone in 6 months (through stress actually) and she didnt say a word. People i didnt even know at work were asking me if i was ok, but my mum ignored it. She struggles with her weight and has never changed her hair.
-Regular backhanded compliments: "thats a nice top - that shape helps hide big boobs doesnt it?" 
Thanks mum.
-In my 20s my ex and i got into a bit of debt (kids were young, mortgage ect) and when we told her about it she gleefully squawked "Oooh no more holidays for you then!" I'll never forget that. The only holiday we'd had for 11 years was an anual week in Dorset in the in laws caravan! I mean whats that about??
-Criticising the kids. And now their BFs!
-Making me feel guilty or ashamed to do anything she didnt do. When i announced i was pregnant with my 2nd DD she said "and this is a good thing?". With my youngest she just rolled her eyes and said "when's this happening then? Was it planned" 
I was married with my own home.
I'm an only child and i've never really talked about this with anyone. Now she's old and its all mixed in with age related stuff i find it easier to cope with somehow. I can feel sorry for her. Even though i've never known anyone else like her it wasnt till my late 30s i began to realise, as someone said up thread, that its not just because she's my mother that she's like this, its something a bit more complicated. I'm not and will NEVER be like this with my DDs.
Sorry for that great rant.
Some of what she's said or done has been rattling round in my head for years! She has her good points and i love her, and part of me feels bad for taking about her like this. But boy that felt good to get that out!