Cable's Lifetime network says the actress will make a cameo on a special edition of the franchise, "Project Runway: All-Star Challenge."
She will help set up a design contest for eight top contestants from past seasons.
The special airs 8 p.m. EDT Thursday, just before the long-awaited debut of the series' sixth season.
The series has been delayed by a switch of networks and ensuing legal action.
"Runway" regulars Heidi Klum, Michael Kors, Nina Garcia and Tim Gunn will also appear.