A Question About Bullying (Maybe) with a Long Story (Definitely)

Lurker posting first question hoping for some wisdom to steer me in the right direction.

Preface: I am Asian and married to an Asian (I'll call H), with a 5 yr old DD.
Place: H's co-worker's party with other people from his office before DD was born.
What happened: Some time during the party I was in a room with one of husband's co-worker (I'll call her RW), a woman who was half Caucasian and half Vietnamese with a Vietnamese name, and the host's wife (NP). When NP welcomed us and introduced herself we took turn to introduce ourselves. When NP asked why RW's name sounded Asian when she didn't look Aisan, RW explained and thanked NP profusely for saying that she didn't look Asian and that she felt sorry for people like her sister, who looked Asian. I didn't react because I knew enough about RW to know that the remark was not out of character for her. NP was mortified and dragged me out of the room and kept offering me food and drink.

As I've mentioned before, I didn't react to RW because it was pretty much what I expect her to say. What I didn't know at the time was just how mentally ill she was. What RW said in front of me was actually a way for her to tell if I could be manipulated and trained to be at her beckon call. Well, my silence was a mistake. After the party she started to ask me to hang out with her. She would call constantly and ask to come over, when she was already outside the door (living close by...sigh). I've always refused politely. Then she did what people who knew her said was her old trick, to cozy up to someone to spite another, she targeted my husband to bully me. Turned out H also felt very sorry about being an Asian and often belittle other Asians, and became more verbally and emotionally abusive to me (there is another long story behind this so I won't try to post here). I was sad for a while because I didn't know why he behaved the way he did but now I understand that it was also not out of character for him, thinking back to why MIL doubted everything he said to her and why she seemed to favor BIL, and why most of his relatives thought he wouldn't amount to anything.

Concerns: DD is 5 yrs old and looked to both parents on action and reaction, and right now she's seeing that the abnormality surrounding her as normal. H is spineless and a pathological liar. RW needs H to do her job because her husband, who was doing her job, left her (according to the contractors who worked at the company before, RW often cried in her cubicle because she couldn't figure out what to do). I have no doubt that H will hurt DD if RW tell him to or to prove that he is not a cheating liar (to RW...rolling eyes and yes, he's made a point to let me know that he couldn't care less about DD) and I don't know how to divorce H and cut off his ties to DD at the same time.

Sorry for the long post but this situation is such a mess in my head that I can't keep it short. Right now I feel I'm the one keeping RW from DD because I'm with her 24/7, unless she is in school (which I volunteer in so everyone there knows me by sight). I feel that DD will be in danger if I divorce H, because I consider H and RW as one big ugly package and I won't be able to protect DD during visitation with H, assuming I get custody and he gets visitation.