Answer:
She dies of a broken heart because of her unrequited love for Sir Lancelot.
Step-by-step explanation:
She is a character in the Arthurian legend, the lady from the castle of Astorat. She is in love with Lancelot but it's not reciprocated by him, that is what is called unrequited love.
Elaine falls in love with Lancelot when he fought Arthur´s tournament on behalf of his father Sir Bernard of Astolat. He wins the tournament but got wounded and ends up in the bedchamber of her until his strength returns. When Lancelot is finally recovered Elaine asks him to marry her but he refuses because he is in love with Guinevere. After that, she dies of a broken heart but left instructions to her family to laid her corpse in a boat with a lily in one hand and a letter in the other, and floated down the Thames River.
I hope this answer helps you.