Traditional Hindu culture uses clothing and jewellery to mark a woman's marital status. Married women wear bangles of red or green glass, bracelets of gold or conch shell, and/or a ma.ngalasuutra, a gold necklace with black beads. There is of course much regional variation. For example, a ma.ngalasuutra is not customary in Bengal, whereas a shell bracelet is. And women from more cosmopolitan backgrounds may not feel the need to signal their marital status via their choice of clothing or accoutrements. But in much of the country it is typical to have some such markers of the woman's status as a wife, and they're also typically understood across communities. A Bengali person would readily know the significance of a ma.ngalasuutra, for example.
These markers all removed if the woman's husband dies. As Naidu's poem describes, the necklace and bangles are typically broken and discarded. Another custom, rather less prevalent now than it used to be, is that the widow also gives up colored clothing and wears all white. White garments are associated with death and funerals throughout South Asia: the corpse is clothed in white, and the funeral attendees wear white as well. Shrouds are also white.
Naidu makes the connection between the white clothing typical of widows and a white shroud. The widow is clad in white as in a shroud, but because she is alive, she is wearing a "living shroud".