They call and ask to speak with her, and suddenly she's talking about flight records and backdooring software... admittedly the stuff about having teams in multiple cities looking for her was a little disconcerting, but if they wanted to arrest her or coerce her into something shady they'd have done it, and probably quickly and not very politely.
I'd have just assumed they were investigating a case that was tor related and either 1. Didn't know enough to understand that she wasn't involved just because she contributed to the software or 2. (less likely) Wanted her opinion on some of the tech specifics of how Tor works.
Maybe just show up to meet them, with an attorney (of course!) and if they start asking anything serious the attorney tells you to shut up and you leave.
It sounds to me like the agents were doing their jobs in their normal, properly secretive if a bit ham-fisted way, and this person totally freaked out.