When Arwen was young 14

Young Aragorn sought out Arwen later, and found her still weeping from the birching she had suffered. "Here" he said, "let me put some of this athelas on your sore... ummm... skin. I've found that for me alone, it heals almost anything." The weed (known to some as kingsfoil) indeed soothed her pain and healed the marks of the cruel twigs instantly. Arwen stopped crying, and Aragorn managed to apply the salve without seeing enough of her naked beauty to put him into a paralyzing spell again. Arwen enjoyed the sensation of his soothing hands very much, and was overcome with gratitude and affection. Aragorn in turn felt a protective love that would last a lifetime.