Backstory: 2 years ago, my sister kicked out her boyfriend. I'll call him DB. DB cheated on her several times, got another woman pregnant, refused to work a "real" job so he didn't have to pay child support on his other 3 kids, got drunk all the time, and beat the crap out of her.
After a lot of coaching and crying and shoulder-leaning and several midnight visits for me to get her the eff out of there, she finally kicked him out.
A few weeks later, she found out she was pregnant. Somehow she was convinced that the baby was his. The next thing I knew, they were not only back together - but they were getting married. I expressed (noholdsbarred) my feelings about it, but I went to the wedding anyway because she is my sister.
A week or two after her wedding, we stopped talking. And we went almost a year without barely saying a word to each other.
One day, she called me up and pretty much told me that she wants us to be sisters/friends, but she can't talk to me about DB any more because she knows I don't agree with the relationship and she doesn't agree with me. She will defend him to no end. And she just doesn't want to go there.
So that's how our relationship has been. 90% of the time OK, basically just leaving out any mention of DB because she knows how I feel and she doesn't want to hear it.
Now, I know that DB has been getting worse lately again. She's not directly telling me anything, but it's not hard to figure out. A few weeks ago, she told me that she wasn't speaking to her mother any more because apparently her mom went off on her about DB and told her how awful he was for her and that she can't support the relationship.
Then, she was in my wedding and we spent a lot of time together over that weekend. He was blowing up her phone and acting like a douche for the whole weekend, all pissed off about everything. (Seriously, he screamed at her for looking at the guy she was walking down the aisle with.)
And then yesterday, she posts a FB status update about what a horrible weekend she had. She said she managed to both break a rib and lose a tooth over the weekend. She didn't say how.
Now I'm getting really worried about her again. But given the history, I don't know if it's anywhere near my place to say anything or bring it up. There's a very good chance she will just shut me out and stop talking to me, if I don't approach it carefully. But if she's in trouble, I feel like I need to do something. H kind of gave me a blank stare last night when I asked him, so now I'm asking you ladies. Any ideas?

CN: I'm starting to suspect that my sister's POS H is beating her up. Sister told me several years ago that she doesn't want my opinion on her H because she knows I don't like him and doesn't agree with me. I'm not sure what to do.
TIA, ladies.