If it is a sprain, isolate her somewhere small and quiet with soft bedding and food and water within reach. Plenty improve with rest alone. Visible break or no improvement in a few days and that is us.
Two more causes to have in mind. Frostbite in a hard winter, which shows as discoloured or blackened toes, and nutrition in keets, who grow fast and need high protein. And if several birds start limping at once, or any of them look otherwise ill, ring somebody rather than examining them one at a time.