I haven't read the responses yet, just wanted to share my experience.
My mil is an alcoholic and a lot if what you wrote is the same. She's always liked a drink and would have a few glasses of cider every night, but the last five years have gotten out of control, I noticed it before anyone else and spoke to dh about how I could smell booze on her when she was picking her dgc up from school, how she'd sometimes be slurring. Bil and SIL both rely in her for childcare and see her everyday so I think it wasn't so much as they ignored it, but that because it sort of got worse over time that it wasn't as prominent to them?
Dd didn't really spend that much time with mil, because she scared her when she talked funny and she would cross dds boundaries like grabbing her for a hug when she knows dd doesn't want hugs.
I spoke to SIL about it and she tried speaking to her Mum, but she'd minimise it and sometimes get angry. SIL still used her for childcare and I'd be popping round all the time because I was so worried she'd have an accident or a fall. Dh had both agreed that she'd never be looking after dd under any circumstances, mil would turn up sober and drink while she had the kids, I loved her but didn't trust her. She never once asked if she could have dd so I guess it suited her.
She would hide booze around the place, she would be always asking to borrow money, she would be sat with no heating or food in winter because she's bought booze, her personal hygiene went to shit, her home smelled of piss because she stopped walking her dog, she turned up at assemblies and sports days drunk and heckling, she's emptied lit cigarettes in bin and almost burned her house down.
She was so drunk picking kids up she couldn't stand and a woman had to carry her home because she kelt falling over, it was a day dd wasn't at school and I felt like shit because I'd never have let her take the kids, I'd have took them off her. I was worried she'd be found dead in her bed, or that she would die while looking after the children, she was on a lot of meds that she shouldn't be drinking with and I was worried that she'd overdose because she was so drunk that she'd forget what she's took. There's so many more incidents and the whole thing is exhausting.
It came to a head when she just quit drinking as she had no money and no one would give her any, she started hallucinating and ended up in hospital. She was so close to dying and it gave everyone a massive wake up call, she spent a few weeks on a dependence ward and seemed to be doing well, she wanted to be sober and wanted to be her old self, she went to AA and started looking healthy, although she had a blip and drank a few days after leaving hospital for a few months she was doing really well. She started looking after the grandkids again but I'd said to dh I want her sober for more than a few months before she has dd, he agreed. I think it takes longer
It didn't take long and I started noticing the slurring again, the smell, the mannerisms, sil told me it's her meds but I just knew. It became clear she's drinking again and Its building back up again, she's looking unkempt, I know the woman who works in off license and mil is in there everyday and the whole cycle is starting again and there's nothing I can do but watch. Shes stopped trying to hide it now and it's looking like she will be stopped from looking after toddler niece.
You can't help her unless she wants help. Mil quit because she had no money which seems to be the wrong reasons. I've read a lot and when there's no impact there's no need to want to change if that makes sense, mil lives alone, she still sees dgc, her family are all there for her and her benefits have been increased so she has more money now. Her drinking life is the same as her non drinking life so why change? I love her but I'm very angry with her too. During the time when she was sober she knew how much she had hurt everyone, especially her grandkids, and she chose to start drinking again. It seems to be escalating quicker as she's not hiding it now, SIL and bil have talked to her, they've shouted at her, they've fallen out with her, they've offered her all the support in the world but if she doesn't want to stop, she can't be forced.
I cant tell you how to help, I don't think you can, nor can your dh or his siblings. I would not have her alone with the dc under any circumstances. She may have sobered up before you went out but addicts are devious and lie,my mil would have booze with her and drink in bathroom. Things will get worse as her tolerance builds. She will decline regardless of anything you do or say so do not blame yourself. The detach advice is helpful and it's what dh, SIL and bil have all started doing. Mils drinking has no impact on her life, but it's had a massive one on everyone else's and detaching is our only option now.
You can PM me if you ever want to chat 