.. Why do they keep talking about "diffusing" bombs?

Oh, it's a common mistake, though I'm surprised Nancy would make such a mistake. To defuse something means to make it inactive and get rid of the fuse; to diffuse something means to spread it evenly throughout a wide area. I would really MUCH rather defuse a bomb than diffuse it.

But hey, she's under a lot of stress here. She's entitled to make a mistake or two.