She's not that bad, just a self-absorbed whiny martyr sometimes. Always plays the victim if I am upset. She is ok with the kids, she doesn't see them alone really, just social/playing etc. I see her every fortnight or so, talk to her in the phone maybe once or twice a week. she thinks we're really close but she knows nothing about me really, she has this 'daughter' in her mind which I don't think necessarily corresponds to the actual person.
I don't want to talk to her about any of this, nor do I want to break contact or anything, she isn't horrid. I can't distance myself any further, I didn't reply to a text last night & already have had needy 'are you getting my messages?' by 9am today.
I have never been at all close to my dad and he will always always take my mums side in any disagreement".
Actually a "self absorbed whiney martyr" type could well be a narcissist in terms of personality. Also your Dad is playing a role in this; like many weak men he is the bystander here and has also failed to protect you from her excesses of behaviour. His attitude is basically, "suck it up child, I will not protect you from her. Am too busy because I want to do self preservation and need a quiet life".
I'm not surprised to read that currently at least you do not want to break contact with her but she is indeed horrid and she is giving you rages inside. It needs addressing and a good therapist would help. However, these people are like shoes and you need to find someone who fits in with you. The first person you see may not do that and also you need to find someone who has no bias about keeping families together despite mistreatment.
You have come to regard her behaviour as not horrid and "normal" but I tell you now all her behaviour is typical of how a narcissist would interact. She is not at all interested in you and/or your children really is she?. Its probably painful for you to see her so call interact with her grandchildren.
Her own image of you as daughter is likely to be very different from how you see yourself as her DD. No wonder you are angry, do you feel like you are your own person (probably not) or do you feel like your mother tried to mould you in the image that she always wanted you to be. Do you still seek her approval?. I would read up on NPD and see if any of that fits in with what you already know.
I think you would be an ideal visitor to the Stately homes thread; it would not do you any harm at all to post there. Do think about it at least.