It says the quote comes from a Mark Frost AI (author interview). So it's via his own interview with Mark.
Sadly, AFAIK she never has—and never will, as she passed away last year.
The real question I always have when thinking about the Mulholland Dr. pilot is: who would've written the show with David if it HAD gotten greenlit? There's seemingly zero percent chance he would have been solo-showrunning a network show by himself, and writing all episodes by himself. The Olson Frost quote is suggestive perhaps that Frost may have been pulled in had the show got greenlit, but that's doing some leaps in logic. It's a mystery, and one of those things I wish someone would ask him when they interview him (instead we usually get the zillionth repeat of the same basic types of questions we're read his answers to a zillion times).
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