I thought she was on a wheeled stand with slightly oval wheels to give a bit of a walking feel to it and she could move it forward with a mechanism operated by tail movement.
My mermaid ingenuity will get me nowhere in life fast.
Floating some millimeters
Wakasagihime's Secret
It looks like she's standing normally, but in reality she's floating slightly in order to walk (?) in the Human Village.
Even moving around is a hard time for Wakasagihime.