Harry Potter and the Goblet of Fire
Gabrielle is Fleur's younger sister. The merpeople choose to hold Gabrielle underwater for Fleur to come rescue during the second Triwizard task. But Fleur gets tangled up in grindylows and can't reach her sister in time. Harry's rescue of Gabrielle breaks through Fleur's arrogant self-importance, and she becomes much mellower and nicer as a result. Fleur is incredibly grateful that Harry saved her little sister, and even gives Harry (and Ron!) kisses on his cheeks.