This determination was depicted more strongly in the film than in the book in several ways.
One example that indicates Catherine's (Olivia de Havilland) strength of character is her reluctance to give up Morris (Montgomery Clift), at her father's (Ralph Richardson) request. Even though Catherine said she would never go against her father's wishes, she did not back down when he demanded she let go of Morris. Certainly she was resistant in the book, but seeing the actress actually play out her feelings gave the character a greater sense of strength.
After being whisked away by her father to Europe on an extended trip, Catherine learned that her feelings were just as important as her father's. This was blatantly depicted in the film and not in the book. In the book, the reader is not sure if Catherine ever realizes the importance of her own feelings.
A second showing of Catherine's determination in the film came when Morris left her
sitting in the house waiting for his return. Even though this was not in her best interest, Catherine was determined to believe. From this point on the viewer can recognize an obvious change in Catherine to indicate her strength. Her clothes changed, her hairstyle became more rigid, and her composure grew more cold. She became a hardened woman after Morris had defied her, and he
realized this upon his return.
This is the final display of her immovable strength of character. When Morris returned to ask her back, she let him know in no uncertain terms that he had greatly messed up long ago. She got revenge on Morris for all the years that she had suffered in silence. Her actions in not answering and having the door locked by the maid, Maria (Vanessa Brown), in the final scene showed her strength. Her ascent up the stairs was also a remarkable showing of her power. She was able to leave the man she so truly loved, screaming and banging for her, when the viewer knows that she is hurting too. That takes real courage, and Catherine Sloper had it.
Catherine Sloper, especially in the film, proved to have a great deal of strength and will
power. I think she is greatly to be admired for maintaining such strength after having lost so much during her lifetime. She was a very admirable character and deserves more study. Clearly if one looks further and deeper, one will see what she truly represents.