This lazy bum can only drain the moisture from things by physically wringing them out with her hands, so a clear restriction on her power is that she can’t drain things that are too big. And those left juiced by Smoothie are still living and can move.
Meanwhile Crocodile can dry out things with a touch of his hand, victims are left immobile and if he wants he can turn them to sand. Not to mention he completely outclasses her when it comes to the range and scope of his thirsty power.
Smoothie would recognize the difference in their strength and submit to the one man she can’t forcefully drain. If she’s lucky he’ll let her try to drain his other hook.