As things stand today, she could be sentenced to 110 years for what she's already pled to; she's really got to make the prosecutors happy if she ever wants to live outside again.
Edit: One such article for illustrative purposes: https://www.popehat.com/2013/02/05/crime-whale-sushi-sentenc... . In this case, the news-headline number is "up to 77 years" and the plausible range Popehat calculates is 2-2.5 years.
She's pled to a set of felonies that each carry stiff penalties. A judge would apparently be within the law and federal guidelines to decide that an appropriate sentence is somewhere between the sentence for any one of the charges and below the sentence for running all the sentences consecutively. It's really easy to get sentencing guidelines to arrive at over 100 years for multiple felonies, if you stipulate consecutive sentences.
One notable exception to the typical kid-gloves treatment of financial crime syndicates was Bernie Madoff, who was sentenced to 150 years, the top of the sentencing guidelines.
The DoJ doesn't typically claim as far as I know that they will stop prosecution in other countries.
I wouldn't call ~20 years into the _future_ "already done". But definitely think long and hard about any agreements you sign in an adversarial situation.
TBH, the guys not even an American so I don't think he really has a right to stay in the country after his sentence is over.
[1]: https://en.wikipedia.org/wiki/Paul_Le_Roux#Trial_of_Le_Roux
Allow Caroline to testify in exchange for lenience. Share that... so that at some point in the future she can be extradited. All good now! As far as I can tell your criticism has no practical bearing on achieving these ends.
Or you might want to be confessing to a country you're a resident of so that you have actual standing to oppose being extradited.
Maybe there is some way she can avoid extradition from the US, I'm not sure, but I have a feeling such a greedy soul could be lured to some other country in promise of riches only to be escorted by men with badges for a nice cruise for a Caribbean vacation.