The lady in The Lady of Shallott, symbolically represents the conditions that existed in society that controlled the lives of Victorian women. As sons were gaining more freedom in upper class families, daughters were still considered possessions to be guarded and controlled by the Victorian family which was ruled by men, fathers, uncles, grandfathers, or male guardians who made all decisions for young women. The imprisonment in the tower could be viewed as a metaphor for maintaining the young woman's purity, by keeping her out of the real world of temptations.
"Possibly the most important, and most broadly felt pattern dominating the life of the Victorian woman was what the reformer Jane Addams once called the "family claim." According to the family claim, women, far more than men, were regarded as possessions of their families."
As a metaphor for the life of a Victorian women, the lady is held prisoner in a tower, which could be symbolically viewed as her "family home," where she is bound by a curse which is also symbolic of the control that her male protector imposes on her. She is restrained from engaging in any illicit romances because purity, modesty and virginity were key to a Victorian woman's potential marital arrangements. So daughters were held captive in their homes, protected, guarded until a suitable marriage arrangement could be made by her father or male relative.
"The poem's popularity rests, more than anything else, on its embodiment of the highly complex Victorian conception of woman, and the correlative Victorian attitude toward the home. The overwhelming problems Victorian England faced created a psychological need to retreat into the safety of the home where delicate spiritual values could be protected and preserved."
The lady in the tower, or the escaping teenager, leaves the confines and safety of her home to seek romance, looking for her knight in shining armor, Lancelot, she runs away from home longing to be embraced by love. She breaks the rules of her family, society and reduces her stature as marriageable material, figuratively she is dead in this society, marked by a stain.
The lady dies after she leaves the tower, figuratively the young upper class Victorian young woman who escapes from her family home to seek adventure and romance with a dashing knight could be considered dead to her family since she has betrayed their trust and ruined their reputation. Imagine if in "Pride and Prejudice" Lydia Bennett, through the intervention of Mr. Darcy, did not get properly married to Mr. Wickham, she would be socially dead to her family, killing all chances of a proper marriage for herself and her sisters.