The assistant-turned-mermaid sits on your lap, her boneless tail occasionally flapping against your leg as if trying to swim in air. She suddenly cringes a little, and then looks straight into your eyes. "Now, you're a nice fellow and I'd love to sit around a little longer...but I'm drying up here and don't know where to find nor how to reach the nearest body of water in my current position, as you may have imagined. Dragging myself around will be way too slow for my purposes, so I have a proposal. Either you carry me to water and I will reward you...", she takes on a more menacing glare now, "...or I will provide a more direct incentive by requiring you to find water as well, if you know what I mean." You give her a dumbfounded look at the latter statements. She sighs and hrms, "let's just say I'll be getting creative with your form otherwise."
A tough decision. You'll either have to lug her around for who knows how long, or you'll be dragging yourself to water with her in tow...