You can say and do literally anything online. I'd need empirical proof, like the actual OP posting photos with the girl more or something substantial. Not a fucking twitter/X reply to a screenshot of a reddit post from a rage-bait farm.

Until then, this is a hypothetical situation. But in this hypothetical situation, we know there is at least one person behind her. We can estimate there's at least not enough people to spill into the main area based on the remaining space in the photo showing the last section of the line empty. We gather that data based on a reliable presumption that the neighboring line-ups are fairly identical. At most, anyone behind her is feeling the mad breakdown of societal rules stripping away and beind made fun of in the actual post.

The only context I'm missing is airport procedure, it's been awhile. I don't know if one must line up at a specific line for departure check-in.

If she was actually causing problems and being snarky about it, I'd be on that drama. I just don't see the evidence for being mad, especially for people feeling a little anxious over something that's probably relieving her of anxiety. Fuck lines and chill out until it's time. Moving will not change the fact you have to wait.