Identifying the Central Theme of Mia's Novel

Read the following paragraph:

In her latest novel, Mia explores the themes of friendship and sacrifice. The protagonist, Sarah, must navigate her relationships with her friends while facing difficult choices that test her loyalty and courage. As she encounters various challenges, Sarah learns that true friendship often requires personal sacrifices for the well-being of those she loves.

Based on this paragraph, what is the central theme of Mia's latest novel?