Does Dorothy take off her slip?

Yes

"If you insist, Scarecrow," said Dorothy. She quickly slid off her now oil-stained white slip and placed it upon the ground.

"Perhaps you should remove your underwear too," said the Scarecrow.

"Scarecrow!"

"Just a suggestion."

"Well, it wasn't a very nice one. Still. I really would hate to get oil all over my undergarments as well. Just turn around."

"Okay, Dorothy," said the Scarecrow.

Then when he turned back around, the Scarecrow could not help saying, "Gee, Dorothy. You must be a lot older than you look."

"Never mind that. How are you coming with that Tin Man?"

"Almost finished."

"Good," she said. "It's about time things go my way for a change."

At that moment, a large animal swooped down from out of the sky and took the clothes Dorothy had so carefully laid upon the ground. To Dorothy, it looked like a flying monkey -- and indeed, the next thing it did was fly off toward the west with Dorothy's clothes in its paws.

"I guess there's no point in bothering too much with that tree now," said the Scarecrow.

"Oh, shut up, Scarecrow," said Dorothy.