Pearl and May, sisters who are the protagonists of Shanghai Girls, endure a great deal together, including fleeing from war-torn Shanghai as the Japanese are attacking the city, immigrating to California, and facing racism in the United States. While Pearl is certainly close to May and they share a family history, May is a problematic figure. She has a secret affair with Z.G. Li, who Pearl is in love with, and May winds up pregnant with Li's daughter (Joy), who Pearl raises as her own. Pearl must deal with betrayal from her sister. Later, May turns in Sam, Pearl's husband, who is a "paper son" (someone who lied about his true father to be admitted into the United States). May betrays Pearl yet again, but it is true that while May knows how to hurt her sister more than anyone else can, the sisters are forever entwined. At the end of the book, Pearl goes off to China in search of Joy. Through Joy, the sisters are forever united, as Joy is May's biological child and Pearl's adopted child. In addition, while Pearl's parents have died, her husband has killed himself, and her child was stillborn (and her adopted daughter has gone to China), Pearl still has her sister, May.
While only you can speak to the relationship you have with your sister (if you have one) and whether it could withstand any type of hardship, it is almost universally true that being "like sisters" and being true sisters are two distinct relationships. Friends who are "like sisters" are usually close but rarely have the history that true sisters have. True sisters often share not only love and friendship but also jealousy and anger. However, true sisters are forever united by their shared past, and most do not separate, even if they experience tension and hardship in their relationships. Their shared history and familial bonds often prevent this type of irreparable breach.