Is Zakat now obligatory on a bracelet that was for adornment, but the intention of its ownership changed due to the owner's illness and another person taking charge of her finances?

The majority opinion (madhhab al-jumhūr) is that jewelry prepared for permissible use is not subject to zakat. Since your grandmother prepared her bracelet for adornment, the ruling on jewelry applies to it, and therefore there is no zakat due on it now, even if it becomes unused, because the zakat on jewelry is waived even if it is not used.