It takes patience and documentation, documentation, and more documentation to do what you want. You also need to make sure that you are doing it for the children, not to get revenge.
Go to the FRTC site at http://www.deltabravo.net/cms/plugins/content/content.php and read the Practical Tips and Techniques section of the Articles page. There are tips there on documentation and a lot of other practical topics.
Keep a journal of every contact you have with the X and/or the children. This is extremely useful in proving a pattern of behavior. Instead of saying in court “she always interferes with visitation,” you can say “she failed to show up with the children on X, X and X date, was 2 hours late on X, hung up on me without allowing me to speak to the children on X, and said XX on X.”
If it is legal where you are, record all conversations.
Believe me that makes a real difference. Especially when they tell so many lies, because it makes it much easier to prove they are lying.
She sounds like a good candidate for “Malicious Mother Syndrome.” Check out the PAS Information Archive at FRTC for an article on this. Also read the article there titled “Family Wars, The Alienation Of Children.” This article lists specific alienating behaviors to look out for and document.
Keep close track of the children’s school records. If she is an alienating parent, the children’s grades and behavior are more than likely going to suffer due to the emotional abuse. School report cards often provide solid evidence of a downward trend while in the X’s custody. That is the easiest way to show a change in circumstances needed to get a new custody hearing.
You don’t have to get down and dirty, you just have to arm yourself with the truth.