How And What To Tell Children
I received the following question a few weeks ago about how and what to tell children about the divorce.

"Here's my problem. I am willing to do anything to save the marriage. I am willing particularly to go to marriage counseling. My wife refuses to go. Our child's therapist even asked my wife to go. She refuses to go so the divorce continues on. On the one hand I do not want to say anything negative about my wife to my daughter. On the other hand I do not want my daughter to think that I was willing, that I willingly gave up half of her life, half of my time with her. And I don't know how to express that to her to make her understand that her father is not another person who has decided to abandon her. That her father is not the person who has decided to give up time with her. I don't know how to say that without it in some way sounding negative about my wife. I don't want to indulge in the lie that so many couples say that the divorce is mutual. We're both decided to do this. We're both happy. This is something that is being completely forced upon me. So I'm wondering what recommendations you might have, how to deal with these conflicting ideas?"

This question hits close to home for me. I was in a very similar situation. My wife wanted the divorce and I was doing everything in my power to save the marriage. Like your wife, she refused to go to counseling so I went on my own. When it came time to tell the kids, I did go along with putting up a united front because I was still hopeful she would change her mind and I didn't want to do anything to drive her further away. I covered for her for years before telling my side of the story to my kids. I have regretted this decision many times. It has caused pain and confusion for my kids that could have been avoided.
Speak The Truth
I have come to the opinion that the best thing to do is to just tell your kids the truth, but not necessarily the whole truth. For example, if your spouse is having an affair they don't really need to know, they only need to know that you don't agree with the divorce. You also need to adjust what you tell your children based on their age. A child of three has a different level of understanding than a child of seven, and a child of seven has a different level of understanding than a teenager.
Children Blame Themselves
Many children will blame themselves for their parent's divorce. This is normal but it is something that can be minimized if both parents reassure the child that this is something between mom and dad and has nothing to do with them. If you daughter has experienced feelings of abandonment before, which you allude to in your question, then this can be especially important. She may be inclined to think there is something wrong with her and you need to make sure she knows that is not true.
Avoid Bashing Your Spouse
You are right to want to avoid speaking negatively about your wife. She is, and always will be, your daughter's mother and your daughter loves her. You need to do everything you can to help your daughter maintain a healthy relationship with her. Some of the best advice I received from the DivorcCare material was that the truth will come out. You don't have to be the one to tell you daughter what really happened.
Answer Her Questions
Answer your daughter's questions as truthfully as you can without giving in to negativity. This can be difficult, especially with older children. They can sense when there is more to the story and will often probe to find out what it is you are leaving out. If you are faced with an overly inquisitive child, just reiterate that the divorce was an issue between the parents and some details are private.
Let Her Know What's Happening
One of the greatest sources of fear for children during a divorce is the uncertainty of how life is going to change. Try to give your daughter as much information as possible about how her life will be different after the divorce.