"Why not join me? Besides that we need someone to attend the boat." Honestly, taking a relaxing swim through water that may or may not contain mortal threats is probably not her brightest idea, but she's riding a little high on having survived not one, but two bizarre threats in the TARDIS.

She ducks back under the water and, while she's down there, rubs the last of the makeup off her face. When she opens them again she sees a shoal of glittering fish a few yards away, but on closer examination, they appear to be cooking utensils mimicking fish and not actual creatures. Maybe it's a trick of the light.

Then she swims under the boat, appears on the other side, and flicks water at the Doctor's head. "You'd like it down here. It's very you."