OK,
my DSis and I haven't seen eye to eye for quite some time - the last time I visited her house was in September 2009 when dd2 was a month old. Since then, I've given birth to DS1 - she didn't know I was pregnant with him as I asked people not to tell her. I didn't want her to know. The last time I had any contact with her was in August 2011 when she ruined my DD2s birthday party by starting a massive row with my inlaws 
DSis has 4 DCs, and I love them dearly. I have maintained contact with them even though I haven't had any contact with her.
At the beginning of the summer hols, DSis was admitted to hospital with some unknown illness. My parents begged me to make contact with her, and I did - for them, not for me or for her, but for my parents.
She was discharged from hospital (without a diagnosis) and we met for the first time in 12 months at my parents house. She met my DS for the first time and it was fine.
On Monday this week I took a trip up to her house as it was her DC3s birthday on Tuesday and I wanted to make sure the card and gift was on time. DSis was not expecting me and immediately upon entering her home I felt very uncomfortable - nothing I could put my finger on but very uncomfy.
Her DCs 3&4 told me upon my arrival that I shouldn't use the downstairs loo as mummy has been sick in there and it smells. DC4 also said that Daddy was still at work and he wasn't coming back.
Alarm bells started to ring, and I just felt that she wasn't herself. I thought she had been drinking, but talked myself out of that as I know how ill she has been. DCs asked if me and my DCs could stay for tea - DSis said we must and she would go and fetch takeaway. At this, I said we simply couldn't and had to get home.
I left after approx 45 mins.
On the way home, I called my parents and started off a whole chain of events which I'm devastated by.
I told parents that if I didn't know better I would say she was drunk - parents didn't believe me, so took a trip up to her house unannounced. The shit really hit the fan.
DSis denied drinking, but her whole attitude and demeanour gave her away. She attacked her DH, our parents and all in front of her 4 DCS who were screaming at their GPs to leave as they were making everything worse
It gets worse.
On wednesday, I got a call from DM to say I needed to pick her up ASAP and get to DSis' house.
On arriving there, we find, DSis sat in a heap on the floor covered in her own vomit. The living room floor covered in vomit with the youngest DCs playing in it and the family dog eating it
She was so out of it - sat there in just a bra, completely oblivious to her surroundings. This was at 5pm.
She had collected her children from school in the car in this state (but dressed) just over an hour before. Eldest DC had called her Dad to say they desperately so needed help as mummy was so ill. Daddy called GP and so on and so forth....
Dsis is fighting drunk. DCs are witnessing everything (and it was obvious by their reactions that they've witnessed it before).
Because of her recent stay in hospital, her DH and my DM thought it best to take her back to hospital - she is denying all the time that she has had a drink.
At 10pm last night, she was still twice over the legal drink drive limit - she wasn't fit to be seen by the MH crisis scene until after 2am.
She was vile to the hospital staff, DH, DM - everyone really.
It then all came out. She has been drinking in secret for YEARS. She has conditioned her DCs to say NOTHING by thereatening them with Social Services and telling them they would be taken away.
She has had numerous bumps in her car, and has been breathalysed on one occassion that we are aware of (obviously clear on this occasion). Her DCs finally admitted that mummy often mounts the kerb when driving and they have been covering up for her.
She also has major issues with dependency on painkillers. Again, she has denied this vehemently.
She was sent home from hospital soon after 5am today. She has a crisis team in place who will visit her daily at home. She is on a detox as she is severely alcohol dependent.
She missed her DC4s first day at school and her DC1s first day at Secondary school due to her drinking.
When she arrived home, her first concern was that she didn't want to see her MIL, and after that I received a call to ask if I had seen her iPad as she couldn't remember what she had done with it.
I dropped EVRYTHING last night to go to her and her DCs, and her major concern is updating her facebook status :(
I am disgusted, angry and ashamed of her. Right now I don't want to know her. I am livid that she has risked her children's lives and the lives of others by driving drunk on a daily basis for god knows how long.
I will do anything to make sure the DCs are safe, but I'm not sure I can see her without without giving her a good hard slap 
Is this wrong? Should I be supporting her unconditionally?
AIBU for being this disgusted with her?
Where do I go from here?
She has some deep rooted issues which she had told everyone she was addressing and was getting counselling for - this was also a lie.
I'm gutted
Sorry, I did say it was long.