Sabrina tries to be cool enough that she doesn't look as relieved as she feels, but she suspects she's unsuccessful.

So she rolls with it.

"I want to make sure you know," she says, "how serious I am about this. How serious I am about you, and making you happy." Having come to grip with her nerves, and feeling some measure of calm, she's able to keep some of the newfound tranquility to her, staying solemn and warm.