The OP said:
So, I've known my DIL since she was 15, she's lived with us too, we've always got on brilliantly together, shopping, lunching, pubbing lol, we always got our hair done together, we got tattoos together. I'm just giving you some background really, and me and my son were her birthing partners.
Cannot help but wonder if the extraordinarily close relationship you had with your sons girlfriend didnt p* the hell out of her mother, especially if, as a truculent teen, the girl may well have used her relationship with you to manipulate her mother. It sounds frankly like a weirdly close friendship not respecting boundaries, and having you present at the birth, if she excluded her own mum, must have deeply hurt her mum.
Of course its a shock that she's now turned somewhat hostile, but given the background I am not surprised if her mum dislikes you, and is discouraging contact, and perhaps the girl, looking back, regrets the closeness she had with you.
Its really tough on you of course, as your motives at the time, were presumably, based on a liking for the girl, and enjoyment of her company, but perhaps with the benefit of hindsight, you can see the hurt that you probably caused.
Is there anything you can do to heal the relationship with your co grandma? I think that may be critical here.
Scottish political mess. Is Devolution working?
I’ve just finished a jacket for my grandson