Jane clearly indicates that in spite of her disappointment in her hopes for Bingley and her friendshop with his sisters that she nonetheless chooses to continue to think well of people in general because to do otherwise will make her unhappy. This is who she is. She is not allowing herself to be taken advantage of but rather maintaining her serenity and integrity in spite of their failings.
"But I will endeavour to banish every painful thought, and think only of what will make me happy -- your affection, and the invariable kindness of my dear uncle and aunt."