{Sigh} DSD is 19. 4 years ago she was quite seriously assaulted (bloke got 13 years), ever since then she has had a massive problem with alcohol. She would have massive binges, then the come downs, turning up in the early hours so drunk she couldn't walk and being propped up and brought home by her friends. DH and I were always obviously woken up by her friends so she could get in.
This has slowly got better over the past 2 years. She still has "moments" like this, but they're a lot more few and far between. When she does have these episodes we have mostly been sympathetic and supportive (although behind closed doors DH and I have ranted and raved at each other, especially as it has disturbed the dds quite a few times). As we are under no illusions that she wouldn't be behaving like that if she hadn't have been assaulted.
She has a somewhat tempestuous relationship with her boyfriend who she's been with for almost 2 years. He has had his own amount of pain (his dad committed suicide a few years ago), so although sometimes I raise my eyebrows at the way they treat and speak to each other, I do think they help and support each other. It is actually since being with him that she has calmed down so much.
So about 3-4 weeks ago she was going on a night out with her friends (which is when it usually happens, when she's with her BF he tends to be able to curb her drinking). TBH she had assured both me and DH and her BF that she wouldn't be drinking a lot and it's been that long since she has that me and DH weren't that worried.
I got a phonecall from her phone at 3am, it was her boyfriend. He said he'd gotten a phone call from the barman at the club where she'd been as she'd left her bag on the table. He was out with his friends and not far away, so he went to the club to get her bag. He then phoned her friends who said they'd put her in a taxi, and given her £20 to get home, but she'd gotten out the taxi at the end of the road and ran off. She was rotten drunk. 
He was ringing to find out if she'd come home, which she hadn't.
So worried he said he was going to look for her and would ring me back. Eventually with a bit of luck he managed to find her (how we don't know as we don't live in a small town). She was so lucky he found her when she did, she could barely walk, it would only have been a matter of time before someone took advantage of her. (Which she couldn't have happening to her again)!
He brought her home and she was aggressive and laughing and just generally out of her bloody mind. I had to take her to bed and undress her put her pjs on etc.
She was very apologetic and ashamed the next day, (not to mention sick as a dog AND she had to go to work). We didn't make a big deal out of it and just silently hoped it would be the last time. Then a few days later she asked if her boyfriend could stay a few days as he was having problems with his mum. We agreed and he ended up staying 3 weeks. We didn't take any keep of him (we don't ask DSD for any rent either) and they were both very respectful and thoughtful while he was staying here. (He works shifts, so when he was coming in late they made sure he was quiet when coming in, and the same when he was working early, especially so they didn't disturb the kids).
Then last night DSD was going to her friends flat with a few other friends and they were having a drink. TBH it hadn't even occurred to me that she would get blind drunk as they were staying in. She had a 4 pack of beers and 2 (small) bottles of cider that she'd bought and had put in the fridge. DH saw these when we got back home yesterday evening.
So he asked her if she was planning on coming home pissed again. She said that no she wasn't. So he pushed it (and IMO was a bit out of order) and said that if she was going to get pissed not to bother coming home and he wouldn't let her in, he was putting the bolt on. This aggravated her and she starting shouting at him. He just repeated what he said. She started to square up to him and became aggressive, whilst getting upset and crying. She then hit the fridge with a bit of force and walked out of the kitchen crying (dd1 bless her said "Won't daddy let you go out, is that why you're crying?") Then she started shouting at DH again, and she threw her iphone at him, he ducked and it hit the floor and the screen smashed. 
Her boyfriend then knocked on the front door which seemed to snap her out of it, and he took her upstairs to calm her down.
About half an hour later they left in a taxi to go to her friends house. I did see her before she went and she was still upset. I just said I hoped she had a nice time.
She didn't come home last night, which TBH we expected, she probably stayed in her boyfriend's. She hasn't been home at all today, but she will have to come home at sometime in the next 24 hours as she has work tomorrow and all her work clothes are here, and her car is outside. DH thinks she'll probably avoid him for the next few weeks now. She'll probably come home in the morning when she knows he's in work.
I'm not sure we're we go from here TBH. I suppose it depends on how she is tomorrow when she comes home. TBH I think she owes him an apology for getting physical (especially as it all took place in front of the kids). 
But I don't think he'll get one. He holds his hands up and says he could have handled it better. Will their relationship survive this? They were close before this, as are me and her. Will mine and her relationship survive this? As even though I wasn't involved in the argument, I think she thinks I should have taken her side.