Christie's response was humorously succinct, and, for its recipients at least, disappointing.
Transcript follows.

Transcript
April 20th 1961
Dear Mr. Kittermaster
I'm sorry I must refuse your suggestion, but I don't enjoy this sort of thing — so really why should I?!
Also I don't see why the conferment of a degree should be an excuse for publicity. I am most averse to the idea.
Yours sincerely,
Agatha Christie