I wouldn't say anything. If she's 400lb, she is beyond all hope, or at the very least, beyond your help. Someone that size needs to come to the correct conclusion themselves. Absolutely no one will be able to talk them into it and any mention of her weight in any form will probably break her and create a huge drama. She knows she's fat, but she prefers to wallow in misery because the path to redemption is too hard. If she wasn't that huge, if she was just a little chubby, then I might say something. Fats of this size are completely lost and you can't help them even if you want to help.