Diamond Tiara seems to be waiting for you to ask, so you do.

“Oh, it’s really quite brilliant.” She rubs a hoof on her chest and glances down to admire it, “A true testament to my intellect.”
“Except it was my idea…” Berry Pinch mutters under her breath.
“And I picked you to think of something, so that makes it my idea. Daddy says that’s delegation.”
Berry Pinch can only roll her eyes in response.
“As I was saying,” Diamond Tiara turns back to you, “The help is mapping out the back of the castle and guessing at how the rooms connect. It won’t be perfect, but together with our knowledge it should be enough to get us around.” Diamond Tiara leans in close, “FYI, they don’t know what we’ll be looking for. If it is true, the fewer ponies that know, the better.”

You can’t argue with that. Getting caught in another dimension isn’t like getting caught sneaking a cookie. You’d get in at least twice as much trouble!