I would say that the answer to this is dependent on what you are able to extract from the text in the support of your answer. In my own mind, I see her as a tragic hero. I feel that her fundamental fault is that she cares and wears her emotions without any sort of buffer in between. Her loyalty to both her family and to Hamlet ultimately represents her undoing. I don't see her as weak, but rather as the result of what happens when individuals whose primary instinct is to feel and offer compassion become manipulated at the hands of others, the victims of deliberate cruelty. On some level, Ophelia speaks to the many individuals who are genuinely caring and considerate and whose trust is violated. It is difficult to label anyone as a "tool" or as "weak" when they have the courage to represent their own essence of identity in such a demonstrative manner that takes the opposite of the world around them.
In Shakespeare’s play "Hamlet" Ophelia is destined to be doomed by her love for Hamlet. She lives in a society that requires that she succumb to the demands placed on her by her father and her brothers. She is always caught between her feelings for Hamlet and pressure from her brothers. When her father is killed at the hands of Hamlet, Ophelia feels guilty and alone. When Hamlet rejects her, she ends her life. Even in death she is denied a Christian burial by a male priest.
Ophelia is a tragic figure but not a hero. She simply loves too deeply a man that abuses her love and has been born at a time when men controlled the lives of women.