When she saw him, Buffy's heart did all kinds of uncool things. The clenching was cheating, the worry unnecessary and the irritation at dealing with a newly souled vampire (again) not helpful. Looking at Giles, she ran towards the lost Spike, pushing emotion aside for action.
So unlike her, really.
"Spike, it's okay." She had to find something to cover him. Not that she didn't trust him, she just absolutely didn't trust him.