Just admit it this was the most intense scene in your childood
"You sacrificed yourself for me."
"I love you."
"You're mine," Elsa whispers, low, lifting Anna up onto the dressing table. "No matter what he says, no matter what you think,I'm your sister and your Queen." She pushes the many white layers of Anna's wedding dress' skirt up, icy fingertips trailing across her hips, and idly pulls her underwear away. "My Anna," she blows frosty air over Anna's clit, eliciting a wriggle and a gasp, before lowering her lips to taste, and smirking as she feels Anna's hands wind, oh-so desperately, in her hair.
Speaking of their personalities during sex, I like to think Elsa would be fairly controlling, probably because she doesn't want to lose control again. She makes Anna spell out what she wants in the filthiest language possible (which is a treat to hear from Anna's usually-innocent lips), and urges Anna to do everything she says with the promise of returning the favor (ad more besides) later.
When Anna introduced Elsa to Kristoff, she became rather jealous. In a pin-against-the-wall, ice-cold-fingers-everywhere, sweaty-writhing-panting-screaming-sheets-tugging, "can-he-do-this-for-you?-can-anyone-else-make-you-scream-this-way?", icy-strap-on-and-warm-tongue sense of jealous. The day Kristoff and Anna got married, Elsa went down on her minutes before, and Anna was still unsteady on her feet when the ceremony happened. Elsa, lips wet, just smiled innocently.