IANAL, but isn't it perjury to plead guilty to a crime, when, in fact, you don't believe that you did anything wrong? Pleading guilty is a formal statement to the court that, "yes, I did commit this(these) crime(s)".
There are ways to plead without admitting guilt. I believe that it is called an Alford plea, in which you admit no wrong, but recognize that the prosecution has sufficient evidence to make a conviction inevitable.
If it doesn't constitute perjury, it should.
Why would the prosecutors "extort" her AFTER her guilty plea? I can see her arguing that she was extorted into taking the plea deal, although I would quibble with her application of the word "extort" in this case. If the prosecutors wanted to lean on her, they would do it before the plea deal. After the deal, they have gotten what they want.
I'm sure that the plea negotiations were something like "take this plea deal and agree to testify truthfully against your codefendants (Trump) or we will prosecute you to the full extent of the law". IANAL, but that is not extortion in the legal sense. It is putting pressure on a defendant, but that's what prosecutors DO.
Can the court revoke her plea deal on the grounds that her most recent public statements contradict her sworn statement to the court?