Final answer:
In the case of uncontrollable shaking postpartum, the suitable nursing action is to cover the client with a warm blanket to help stabilize body temperature, with a potential follow-up of contacting the healthcare provider if symptoms persist or worsen.
Step-by-step explanation:
If a client arrives at the postpartum unit after delivery of her infant and is shaking uncontrollably, the most appropriate nursing action would be to cover the client with a warm blanket. This shaking can be due to chills or a drop in body temperature after delivery, and it is a common reaction. The warmth will help stabilize the client's body temperature and provide comfort. While it is also important to assess the situation for other complications by checking the fundus and ensuring that there is no excessive bleeding or other issues present, providing immediate warmth is a key response to the specific symptom of shaking. If the shaking persists or if there are any other concerning symptoms, contacting the healthcare provider would be the next appropriate action. Placing the client in Trendelenburg's position is not indicated for postpartum shaking.