How and when did Helaena Targaryen die in House of the Dragon?

Ryan Condal has proven that he’s not afraid to be bloody and brutal when it comes to killing characters, major or otherwise, in House of the Dragon. That shouldn’t be a surprise given that it’s an adaptation of George R.R. Martin’s 2018 novel Fire & Blood, which, spoiler alert, features many deaths throughout Targaryen history, particularly during the civil war between the Blacks and Greens.