First of all, there is NO inheritance tax — unless her estate is over $11.2 million. So that’s not a factor. The real question is how those CDs are “titled.” If they are in her name alone, the money would be tied up in probate court, possibly for months, and that’s assuming she has a valid will.
The easiest way to solve the problem is to add your name to hers — in joint tenancy with rights of survivorship. So the title on the account would read “Mary Smith and Susan Smith, JTWROS.” The bank will likely ask your mother to provide written consent to add you to the account (to prevent elder fraud, which is so prevalent today). I’m not asking if you have other siblings who might feel entitled to share in this money. If that’s the case, you could open several CDs, each titled jointly with one of your siblings.
The money should remain in short-term (a year or less) CDs in the bank — not in any other investments.
And while I’m at it– you should make sure that your mother does have a current will and a healthcare power of attorney, and living will (describing her end-of-life care instructions). If you don’t have an attorney, you can find one at www.NAELA.org — the national association of elder law attorneys.