Buddy
re your comment:-
"sorry I didn't explain very well but she so far has never been openly toxic like that to dd, in a way I wish she was because I'd then have no hesitation in cutting all contact. If dd called her she'd happily chat to her and act normal, it's me she hates! She gushes over dd but only when it suits her selfish ways to engage, the rest of the time she is either ignoring us with her controlling silent periods, or is playing the victim all woe to is me, nobody loves me apart from my granddaughter. She's 5, to her when Grandma is interested and buys her sweets or invites her for tea she thinks she's the best ever, then gets upset when she goes silent"
Going hot and cold on a 5 year old is a low blow. You would not have tolerated any of that from a friend either, your mother is no different. Your mother is actively trying to buy your DDs affections and your dad enables his wife in these behaviours.
Your mother still hates you but what's tripping you up now is the narcissist's ways of adapting to changing circumstances i.e. you now have a family of your own.They know they don't have the same power and control they used to so they usually switch to sneakier methodologies. This allows you to think that they have changed from what they were when you were growing up.
Your mother has not fundamentally altered; she is simply now using more sneaky methods and she will continue to use your DD to undermine you and your DH as parents.
Your mother is and will now use different methods. The NPD grandparent will use their grandchildren in the same way they would use an inanimate tool. Without regard for the humanity of your child, that child becomes a tool in the hand of your NPD parent to hurt you. This will always result in moral and/or emotional harm being done to your child as well.
The actual mechanics of how the NPD grandparent will misuse their relationship to their grandchildren will vary. Generally, they will either over-value or under-value the grandchild as a means to get to you. Often, when they over-value, it is the objective of the grandparent to steal the child from you. I mean that in both senses, physically and emotionally. Narcissistic grandparents are known for so much trash-talking against you behind your back to your own child or children that they want to go live with grandma or grandpa, or the Narcissistic grandparents simply inspire rebellion of the child against you. They steal the hearts of the grandchildren. Sometimes, they will battle for physical custody of a grandchild after their slander campaign against you has won them powerful allies. Many times they have a lot of extra cash to throw around since they are done raising a family. They may successfully exploit the natural selfishness of the child by using cash or toys to lure them.
And I still would not let your Dad off the hook here because he is simply acting out of self preservation and want of a quiet life. He has and continues to enable his wife's behaviours. In a straight fight he would choose her over you, such weak men often need women like your mother to also idolise. I would see if it is now possible for someone else to take her to school on the days you are unable to do this.
Re this comment also:-
"I also have a brother and want dd to have contact with her cousins, she adores them and is an an only child so I worry when me and dh are gone one day she'll need the only family she'll have left, I can't have any more children and I hate the thought of her losing touch with her cousins"
I think you need to look at the reasons behind that mindset a lot more closely. Your brother here is the golden child (itself a role not without price but he does not know that). What if her cousins are infact nasty people who want nothing to do with your DD going forward, they will go their own way and perhaps leave your DD behind particularly if they are a lot older. It will also need your brother's co-operation for his children to see your DD. She won't need her cousins as an adult, she will have friends and family of her own.
You will need to move and I would say sooner rather than later (certainly not in the year or two before she starts secondary school). You need to put physical distance as well as mental distance between you and these disordered people.