Going back a bit, narratively speaking, to right around when Miss Calculated cant-cursed Miss Chievous, then took a seat on the padded armchair Lucas had previously occupied.
Now that Miss Chievous is the last of the loiterers left vertically aligned, she looks at her lounging possibilities. They are, unfortunately, relatively lacking, as all of the possible places are settled by her colleagues. Left with limited alternatives, she selects the most undeniably logical solution; beleaguering pitiful little ill-fated Jonathan.
Since she at least bears a modicum of respect for the fact that he’s in the middle of playing a game, she sits on the arm of his chair and leans over to look at the screen of his phone, rather than directly physically terrorizing him.