Co-Attachment Parenting Through Divorce?

This will be a breif post but I appreciate as many comments as possible because I feel desperate for any ideas as to what to do. 

I have only one neice (15 months old) whom I adore and am very close to.  She has lived with me off and on and I have treated her in the same healthy, attached way as I always have my own three children.  I don't think much is needed in the way of elaboration to stress how close I am to this little one for anyone who has ever loved a child!

My sister (her mother) hates the idea of anything "attachment parenting" related but due to my time with the two of them and providing insight as well as scientific studies to back it up, my sister gradually adapted to co-sleeping with my neice.  I felt this was a huge victory.  When DN (dear neice from here) was six months old, my sister and her husband split up and my sister plus her baby moved into my house for a couple of months. 

While I was reading to my kids before bedtime in my husband's and my bedroom, I could hear my little sister in the room down the hall, crying and screaming at her six month old daughter to go to sleep in her playpen while the baby just wailed.  Well, that was not going to happen in my house. 

I flew down the hall and threw open the door.  My little sister was sitting on the bed, head in her hands.  My neice was lying on her back in her playpen, sobbing, with tears streaming down the sides of her face.  I scooped her up and started to sway with her.  She immediately tangled her fingers into my hair, and started to calm down, with shuddering sobs.  My sister said she could not deal with the effort and time it took and was just too overwhelmed and I should place the baby back down and leave her to cry; that eventually, as she had every night for the past three months, DN would exhaust herself and stop crying. 

Instead, with a million things I wanted to say but realized could wait until the next day, I offered to keep DN for the night in our bed, with our kids, and my sister could take a hot bath and get a good sleep.  She accepted (I would not have let her decline!) and I took the little baby into bed with me.  She woke up three times that night and I had her back to sleep within minutes, so long as I was holding onto her (she was long ago used to not feeding through the night due to being denied it) and snuggling with her. 

The next day, my somewhat apologetic sister finally came downstairs toward noon, and thanked me for the extra sleep.  She assumed I'd had none at all.  I went on to explain to her why I had gotten sleep with few awakenings and why the baby hadn't been screaming and crying.  My sister was finally willing to listen. 

Over the next few weeks, I taught her as much as I could about the benefits of co-sleeping; how it is healthy and practical for baby and mother; why it is safe; where the bogus myths that it is a danger originated from; and how she could use co-sleeping to actually get some SLEEP without leaving DN to suffer in angst. 

They were co-sleeping champs before long.  Then something happened I did not see coming; overnight, she went back to her ex.  He hated everyone in her family and we could barely see her.  It was a highly abusive relationship.  Without getting into the details (oh boy, there sure are many!) of that (maybe I'll save it for another post), DN's father insisted on putting her back into the crib.  It didn't work so well this time.  DN would be rocked to sleep, placed in the crib for a short while, and when she awoke in the night, my sister brought her into bed with them. 

This routine lasted for several months.  DN's father became more and more upset the longer it went on.  His mother advocated the CIO method strongly.  He couldn't see the harm in it (we came to find out LATER that when alone with DN, he and/or his mother were also double dosing DN on cold medication to make her pass out so they wouldn't have to 'deal with her').

The relationship between this man and my sister, however, did not last.  He ended up leaving and it was just my sister with DN once more.  They immediately went back to co-sleeping and it was a major success for them both.

Currently, there is a custody battle going on for DN.  No matter what, the father will have overnights with her; he is upfront that he will stick her in an unfamiliar room in a crib-jail, turn off the light, shut the door, and just let her CIO. 

My sister is horrified at the idea; I am DEVASTATED.  There is nothing I can do-- is there?  Has anyone else dealt with this?  Is it possible to convince him to do otherwise?  None of the information or tactics I've tried to take have made any difference to him. 

I literally feel sick to my stomach with anxiety over picturing my neice, who is completely used to co-sleeping by now, being placed alone in a dark, scary, unfamiliar place and forced to cry herself to sleep, again and again and again with each visit. 


Have you gone through this?  Do you know anyone who has?  Do you have an opinion on what will be/should be done/might happen?

Any comment/input/suggestion/story/experience is greatly appreciated!