The ONLY place for this money is in a money market deposit account at your BANK, and maybe half in a one-year CD at the bank. This is truly “chicken money” — money you cannot afford to lose. YOu’ll quickly see that she will earn almost NO interest — but she won’t lose a penny! And that’s the most important thing.
One more thought — you should make this a joint account with her, so that if she is incapacitated, you can withdraw money for her care. And also, although you probably have done this, you need her healthcare power of attorney and living will (instructions for end of life care). The time to do that is now!