@Final
Ahh.
Yes. It was already established that she was there. Thus, in danger; her brother knows, and is moving to intervene. So, why single her out specifically?
Perhaps? Targeting her moves it up to a much shorter time frame for action in regard to her safety, heightening dramatic tension; will her brother intervene in time?
The rationale for targeting her is her lunch; the villain is a bully, bullies target peoples lunches, going for her lunch is a way of showing that he's a real badass, in an infantile way it's a bully pulling an intimidation play. It's definitely a stereotypical bully activity. That it's her lunch targeted, can be argued to strain credibility, but metaphorically flexing his muscles during his monologue, not so odd, really.
ETA: Part of why it would increase dramatic tension is that since her brother made the lunch, there's a reason for her making stupid emotional choices rather than just handing the lunch over. It falls into the trope regarding bullies and lunches, that the targeted lunch carries more meaning than just a meal, that by stealing the lunch they steal the love of the person who made the lunch; thus, greater emotional impact upon the victim. Thus, we needed to know about the lunch in advance, so that we already had that background. It's Chekhov's Gun, to use a term from European literary criticism. That's
precisely why it was established in advance that she had it; it wouldn't have been mentioned if it wasn't going to be a plot hook.
But, you may be right, it may just be poor plotting/writing; how the story develops should allow us to determine which it really is.