She was Marcy in Married With Children, and this is the closest she ever came to nudity.
Great collage by Penman
My thought: the obviously real cleavage showing when she appears in her bra doesn’t seem to represent the same breasts beneath the diaphanous gown. My guess is that she was wearing a prosthetic chest in the see-through scene, but I don’t know that for a fact.
Prosthetics confirmed in the comments. Also find there some leads to a possible Bearse topless scene.