Her staring at Xander screamed more 'Buffy mockingly gaze at something silly Xander is doing', she usually did that on the show.

I don't see mocking. Maybe because I correlate this page to Buffy's erotic dream about Xander. And her next close-up shows that she's uphappy with Renee being Xander's "sparring partner". After many sparring sessions with Spike Buffy perfectly realises the implications... :)