"Don't you want to explain yourself?" Zayn is asking again because Stella still hasn't spoken.
As Stella usually is when faced with people she doesn't know, she becomes timid and anxious. Both her hands are now sweating profusely and her eyes are darting back and forth because she doesn't want to make eye contact with the Duke. She's just afraid if she faints there first before saying anything.
The fact that she is someone like that must have been known by his childhood friend who was also in the office, Jeremy. Because of that, he is now also feeling restless for her even though she didn't look at him. She also is far from asking help.
In Stella's mind at that time was that she hoped to be blessed with strength so that the Duke would not suspect anything or be suspicious of her. She also doesn't want to ruin Ariana's plan just because of her anxiety. So, she slowly took a deep breath and tried to look at Duke before answering.
