I believe Tracy was not asked to testify because of the relationship with LP (who, let's face it, with all of his theories that he presents as facts, is a loose canon!). It would have given the defense an opportunity to ask questions about LP that could have taken things off course.
Also, if you listen to her original statement, etc., she had habit of giggling nervously, in mostly inappropriate places. Seeing her recently, she has evidently become aware of that and it is no longer an issue. It is unfortunate, as I agree that she did have some insight that others did not. And...the prosecution was trying to keep things simple but effective. Little did they know the jury was just listening to "flash" and were mostly ignoring the facts. Sigh.