There's an unguarded ventilation shaft, if you're flexible enough to get in. [Mikumo says it rather lightly - it's where she's intending to head in herself, once she's satisfied enough that they have a good cross-section of the outside. This girl looks quite small, so Mikumo figures the ventilation shaft entry would be a good option for her.]

It's entirely possible they didn't figure we'd actually join the resistance. There seem to be plenty of civilians in the camp...and this is a very fast turnaround on another operation after the previous one, considering the organisation needed.

[Delta Flight has to be available on short notice by their nature, so Mikumo's used to that sort of thing, but ideally a mission like this would need more of a lead-up and preparation than this.]