A proffer is a transcribed interview under oath and under Florida law it must be provided to the defendant's counsel (just as ANY statements or other relevant evidence must be disclosed to defense counsel before trial). Development of this evidence before trial is called "discovery" and Florida is arguably the single state having the most liberal "sunshine" laws that require ALL discovery must be made public. This is the default for Florida trials so it ordinarily would be made available to anyone requesting it as soon as it is filed with the court. In this case, however, the defense has cited Florida Freedom Newspapers vs McCrary for the proposition that a court MAY seal discovery if it is the only way to avoid aggravating excessive pretrial publicity.
Thus, the only question here is whether making the proffer public would generate excessive pretrial publicity that could potentially damage Charlie's right to a fair trial. In the McCray case the press was trying to get interviews of jail officials in a case that included rather sensational claims of mistreatment of inmates. The court held an in camera inspection of the interviews in chambers and decided that, yep, the interviews would generate a lot of press and, thus, sealed the materials until trial. I believe the court here will probably make the same ruling because anything Katie said would definitely generate a lot of interest and attention.
On the other hand, I can also see the press has a pretty good argument that there have been two trials in which the Adelsons were unabashedly named as conspirators by both the state and the defense. Moreover, there are podcasts and tons of material already in the public record pointing fingers at Charlie, so I would make the argument that the proffer would not meaningfully alter the dynamics of the upcoming trial.