I will probably skip this character/plot point in the adaption as it doesn't make the heroes of the story seem very heroic.
As for the books, according to the IC wiki:
Galiana was the daughter of Lord Halstead of Aroughs and the sister of Tharos. She died while trapped by the Varden in the chaos after the siege. Later, Tharos swore that he would kill Roran to avenge her.