Thanks for your messages.
Basically, trying to keep the story as short as I can, me and my mum have a long history. Starting with her abusing me as a child but not my siblings. Then as an adult she belittles me, undermines my parenting and started to fill DD's head with horrible things about me, telling her I didn't do anything for DD, that I was a lazy mother, that DD shouldn't listen to me, and other horrible things I won't get into now. I stopped contact between my mum and DD as that was the final straw. I won't let her dare poison my child's mind!
However, I was informed by my sister, who I despise more than my mum, that my mum was getting legal aid to find out her rights as a grandparent and about taking me to court. After being advised by my friend about her friend who was taken to court by her parents who got visitation rights to see her kids and take them abroad on holiday, I spoke to my mum.
She hasn't changed one bit, denying she said anything to DD and that she's done nothing wrong. She mentioned mediation. Like I said, I know that our relationship will never be the same, and I'm well aware of that. But I was considering going ahead with it, not to go into my issues as I wouldn't ever bring those up to her, but more to perhaps show her and to have a third party (hopefully) agree that she can be wrong, and that she needs to open her mind to that.
Saying that, I don't want that to happen so it can at all affect our relationship, as I think we're pretty much done, there isn't any hope. But I also don't want to end up going to court with her and having them decide what is best for my child when I know what is iyswim.