I’m going to have to try and make this as non identifying as possible so please bear with me.
DM has always had mental health problems. Sectioned at one point, on meds for this and seems to be stable.
She has had problems with alcohol, binge drinking and being abusive to my father who left her. There was also domestic violence regularly when I was growing up up until the divorce when I was 16 or so.
My childhood was a misery. Fear, constant worry about the drinking and violence, finding DM drunk on the stairs etc. Every weekend was spent terrified of what might happen or being kept awake all night. Dm however thinks I had a lovely childhood and also thinks she’s been a great parent 
Since the divorce I’ve been NC with father who has since got on with a normal life.
DM seemed to be sorted on the outside. Has her own house and seems happy enough. She put a lot of effort into spending time with and helping me with her DGC and has been a nice enough grandmother. She has helped with childcare etc often and seemed to be doing well. I can’t forgive her but have managed to rebuild some sort of relationship. We aren’t close but can speak.
However, I found out recently by chance she was still drinking heavily pretty much every night. Bottles and bottles of wine. She also let me down quite badly in one of these ‘blips’ which unravelled the whole thing.
Now I can’t trust her. I can barely look at her. She won’t admit it, said she isn’t drinking when I know she is. She just denies it over and over and over despite me having concrete evidence. Once in a drunken conversation she broke down and cried yet the next day had forgotten the conversation ever happened.
I’ve blocked her number and no longer speak to her after 5pm incase she’s drinking but I really can’t look her in the face. She’s constantly posting drunk crap on social media and messaging me things that make no sense.
I don’t think i can get past this, all those awful years have came flooding back and I don’t want my children around that.
The logical part of me thinks she’s only drinking at night so what she does in her own home is up to her but at the same time it’s a betrayal and I thought she was over it. She’s not even supposed to drink at all on her medications.
So where do I go from here. The trust is broken but at the same time she’s been such a good grandparent to DC that I don’t know if I can shut her out for their sakes.
She won’t admit it, won’t get help because there’s no problem so how do I go about dealing with this now?
I’m tempted to ring her tomorrow and just say my piece but will that just make it worse?