This is what bitter (adjective) means: "Feeling or showing anger, hurt, or resentment because of bad experiences or a sense of unjust treatment." (Oxford Dictionaries site) The "fear and suffering" (first sentence in your passage) could have caused bitterness, but the writer said she would not be bitter. She would think of a Manderley which was without fear. Is this passage from Daphne du Maurier's novel, "Rebecca"? Do you normally use a dictionary?

Here it means it will not give you a feeling of resentment or cynicism. It will not hurt you.