I don’t think she literally meant she didn’t know what the sword was. Her expression looked more like do-you-really-expect-me-to-use-a-sword look. She is a sheriff, so of course she is to using a gun.
And with the library, it may have said that outside, but on the inside in looked like it hadn’t been used in years. Also, Emma may be remembering her event with Graham and when he was looking for his heart–I doubt she knows that Regina killed Graham, but I am pretty sure that by now she has figured that nothing in this town is what it seems, and that many of them may serve for Regina’s purposes.
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