Let me say it has been years since I was in law school and also years since I practiced. However, it is one thing for SOMEONE ELSE to prejudice the jury against you. When YOUR OWN WORDS sink your ship, that is mere stupidity. We need a practicing atty to tell us whether you can actually prejudice the case against yourself. Common sense tends to say you cannot. That is why you have the right to NOT testify.
The theories behind "prejudice" are to keep outside forces/people from stacking the deck against the defendant. Not from keeping the defendant from blabbing themselves into a mistrial or a new trial.
ETA: JA thinks she is very smart. I would not put it past her to have "accidentically" blurted the part about her cell in an attempt to try and get an appeal/mistrial, etc.