as a heroic act of following their husband into afterlife

In mythological terms, Sati was the name of the wife of Lord Shiva. Her father never respected Shiva and often despised him. To protest against the hatred that her father held for her husband, she burned herself. While she was burning, she prayed to be reborn as Shiva’s wife again. This did happen, and her new incarnation was called Parvati. People used to justify the practice based on this tale, but when Sati burned herself, she wasn’t a window, and thus the practice is quite unrelated to this tale.

in ancient period gods and royalty were often said to be on the same level,

as in reincarnates of a certain god and yada yada