“If there is dark matter and if there is a disk of the stuff crossing our orbit in a regular pattern, then there might be something to this hypothesis.”
Calling her proposal a hypothesis is extremely generous. It is based on nothing but her imagination. Furthermore WHY she has chosen to propose this is a mystery. Are there no KNOWN and understood mechanisms to explain this? Its well understood that a planet, comet, or other large body passing by an object can change its trajectory. Its observable and testable. Why invoke dark matter? Why suggest it has anything to do with a specific event such as dinosaur extinction? Its bad science fiction.
I am not a big defender of this idea but I can guess an answer to your question: the regularity of the extinction events suggests a regular disruptive force.