After being asked to put her tongue out and told "thank you, that's enough," a patient continues moving her tongue in and out for several more seconds before stopping, seemingly unable to move straight on to the next instruction. What is this?

This is motor perseveration: the senseless continuation of a goal-directed physical action well past the point at which it has already served its purpose, exactly as described here — the tongue movement continuing after the instruction has already been completed and acknowledged. It is not a tic, which is a sudden, brief, repetitive movement unrelated to a preceding instructed action. It is not waxy flexibility, which concerns a limb retaining an externally imposed posture, not a self-initiated action continuing past its purpose. And it is not a stereotypy, which is repeated regardless of context or preceding instruction, rather than being a specific earlier action failing to stop on cue.