Final answer:
The best next action for a nurse caring for a client at risk of hypovolemic shock is to assess vital signs frequently, as it is vital to monitor for any changes in the client's condition and guide further treatment.
Step-by-step explanation:
A client on a postpartum unit who is at risk of hypovolemic shock requires immediate and appropriate nursing interventions after notifying the provider. The best action for the nurse to take next would be to assess vital signs frequently. This is because monitoring vital signs is crucial in detecting changes in the client's condition and in determining the effectiveness of interventions. Administering a diuretic or antihypertensive medication is not appropriate as these can exacerbate fluid loss and hypotension. Encouraging increased fluid intake is beneficial, but frequent assessment of vital signs is a priority to guide further management.