Vader gives her time. He remembers, all too well, his visions which lead him to think Palpatine created him in the Force.

He can't imagine for her. Doesn't want to really. But after a couple moments he mentally reached out, just as the tears start, nudging Kylo hard to physically reach for her. Ground her.

"Rey. Listen. Breathe. Breathe with us." Between Anakin Skywalker and his time interrogating people he knew how to calm someone down.

Vader even reached over, gold-tipped fingers brushing her arm. Come on child.