Well, she's confused about a Lot of Things, including the most basic concepts in science and geology:
First of all, they use carbon dating, as an example, to prove that something was millions of years old. Well, we have the eruption of Mt. Saint Helens and the carbon dating test that they used then would have to then prove that these were hundreds of millions of years younger ...
I have more at the link above, but in a nutshell O'Donnell is mangling two young earth creationists myths together in the fundie blender that passes for her mind, 1) that carbon 14 is unreliable, and 2) that samples at Mt. Saint Helens proved radiometric dating invalid.
Radiocarbon 14 is used to date organic remains less than one-hundred thousand years old, not volcanic extrusions hundreds of millions of years old. Radiometric dating in general, such as the Potassium-Argon method O'Donnell appears to be conflating with carbon 14, relies on dozens of techniques specific to ranges of time, from thousands to billions of years, each based on the same physics that describes how everything from atomic bombs to CAT scans work. Not exactly impressive for someone seeking Senate office in a super power that depends on the applications of science for both national security and economic survival. I'm not sure if I should laugh at her painful ignorance, or make plans to leave the country.