The reason for her silence is that in spite of the media telling us how smart she is, the word intelligence and Hillary Clinton don't go together! :-)
I have a feeling that as soon as the official interview was concluded, the NPR reporter who asked this caught hell for daring to ask Her Heinous something that wasn't on the pre-approved list.
But Mousie, thou are no thy-lane,
In proving foresight may be vain:
The best laid schemes o' Mice an' Men,
Gang aft agley,
An' lea'e us nought but grief an' pain,
For promis'd joy!
Excerpt from "To A Mouse" by Robert Burns