But even if we grant that falsehood, she still does not have adequate reason to withdraw her consent for organ donation, as long as she can present proof to evil consequentialist doctors that she's worth more alive than dead.

From what she said "she'd heard that doctors don't try as hard to save donors in hopes of using their organs to save other lives.", it isn't that they actually kill her if she has an organ donor card, just that they don't put in as much effort. Which implies the following beliefs:

1. Doctors don't try so hard to save those with organ donor cards
2. Doctors do try harder to save those with blood donor cards

The conclusion she should draw is that she should carry just a blood donor card, to demonstrate that she is really useful alive, and not at all useful dead, so they should try really, really hard to save her.