I'm not surprised your older daughters might say they don't need counseling....and they may very well have a good grasp on things (but the affects truly are astounding). I'm more concerned about your youngest daughter and her anger etc. I believe she's internalizing an awful lot of pain and anger and she's most definitely the one who needs to be in counseling.
Ok...so you do stand up to your W when she acts out and you are around, which you say doesn't happen often. So am I understanding you correctly? She behaves inappropriately more often when you aren't present? When I say that I don't mean that she necesarily pre-meditates that's what's going to happen either...it's just when things tend to happen?
If that's the case then you are stuck in a situation where it's your D's words against hers right, as to the facts of events? That would be difficult. BUT...since she has had a history of acting out (verbally or whatever) against the girls....I would assume you probably put more weight towards what the girls say happens....since you have also been on the receiving end of her behavior. If so, then I do see a boundary that needs to be drawn....and I know you are working your way to setting a boundary....you're getting there.
Basically the boundary as I see it would be...."if you feel it's appropriate to yell and scream at the girls and I, if you feel it's appropriate to put your animals before your family, and if you feel you cannot treat us with respect then you need to live elsewhere. I am no longer going to tolerate this behavior from you and I'm not going to allow you to treat our daughters this way. You CAN control your behavior...however if you feel you cannot control your behavior, I am here to help you pack."
Now...of course this is just my way of putting things.....and it's only an example. But I'd say it's a boundary. I threw in there the snippet about packing too...because I'm pretty sure anytime you try to set/enforce a boundary she's going to be likely to throw the "I'm leaving" card.....back on the table. Pre-empt it.
Just my 2-cents. I'm sure others will have better feedback for ya!