I think there's a 99.5% chance this is just the work of some troll, but I just came across this comment on a YouTube video of Marlo Thomas getting pied on her sictom ThatGirl:

Marc Mercadante
(1 year ago)
I was 13 when this episode came on TV. That was it, I was hooked on beautiful women taking pies in the face. She created that scene years later on the Mike Douglas Show but got hit with 4-5 pies as did Rachel Welch. awesome!

Sounds extremely unlikely, as to my knowledge no one else has ever hinted at either of these pieings. But there were at least a couple instances of pie throwing on the Douglas show, including of course the legendary Moe Howard appearance. On Hurley Coward's list of lost pie scenes, there was mention of one Douglas show where Diedre Hall got pied. (Would've meant a great deal to me to have seen that back then. As a 70s kid, I ogled Ms. Hall in her Elektra Woman outfit every Saturday morning...)