Granted as you say not all documents or filings would become evidence, or be used at trial. If her handwritten note had simply stated what her payment agreement with JB was it would not be a big deal. But in this handwritten, notarized, filing to the court, she personally spoke directly about the crime and her guilt or innocence (instead of talking about the actual question that was put forth concerning her lawyer). There is no way that is not being brought in to evidence. It's the whole "anything you say can and will be used against you". As others have said it is an attempt to testify without taking the stand. But I think in this case she probably really screwed herself.
Bolded emphasis added by me.
Again, with all due respect, I disagree.
A document that it notarized is afforded the assumption (rebuttable) that it is what it purports to be without any further need of identification: a document that was signed by the declarant, who, in this case, was Casey. That's the end of the surface "benefits" afforded by this document being "notarized" instead of just being signed.
The fact that it is notarized does not mean that what it says it true, or that the document is relevant, or that the document will be admissible during the hearing on the motion it accompanies and/or any future trial.
Moreover, when an attorney files a motion and exhibits into the official court record, the exhibits that are filed are NOT usually the originals. The original exhibits are maintained by the filing attorney, should he/she choose to introduce them into some hearing/trial. What does this mean? It means that unless JBaez is foolish enough to offer and try to introduce this into evidence during the hearing upon the motion the affidavit accompanies, which MIGHT compromise Casey's right to take the 5th at that time as to the information in the affidavit, or at the future trial, he will have the original and only he may use it.
The SA won't have the original, which is typically required for introduction into evidence (it's called the "best evidence rule" for short) and, more importantly, even if the original had been (foolishly) filed into the official court record as an attachment to the motion, the SA cannot seek to introduce it and then turn around, call Casey to the witness stand and cross examine Casey in regards to it any more than the SA can offer and introduce other of Casey's statements to LE in an effort to trump Casey's right against self-incrimination.
Did JBaez do this in a likely attempt to get this out in front of the media (hint, hint)? Probably so. But it does NOT waive her right against self-incrimination. (The "anything you say can and will be used against you" doesn't apply here b/c why on earth would the SA, who cannot force Casey into testifying by trying to introduce the affidavit into evidence, turn around and introduce this denial into evidence?!?!? They won't.)