I have no in-universe answer, but from my own military experience I would say it's probably because Ferro is a pilot.  In modern military, multiple briefings happen depending on what your role in the mission is, and often pilots get more info than the grunts (they need a "bigger picture") as well.  

Additionally, if you're delivering a mission briefing to the whole group, you've already done some amount of planning beforehand, planning which probably required you to discuss options with your technical experts, eg he pilot.   In one of those sessions, she could have asked the question or heard someone else ask it.  

This is speculation, of course, but I think we'll-reasoned.  There's no way the LT, company man, and their special staff would've delivered that mission brief without some analysis and planning, and that would require the consult I spoke of.