Korra doesn't take any further prompting. Once the shadows disappear, she jumps forward and lands with a solid earthbending move to dig earth out from under the blonde's feet. It's a sizable effort that pushes the limits set on her bending by Luceti, and she's hoping he won't be able to keep his footing. She and Aang had to get him buried before the shadows returned, so she didn't think twice about putting her all into it.