A lot of people have gotten into the habit of calling that a scythe, but it isn't. A scythe is sharpened on the inside edge of the curved blade, not the outside. Also, the edge on a scythe is at right angles to the handle, not parallel to it.

What she has is a head-man's axe.

I'm pretty sure the mochis understand Japanese, even if they can't / don't speak it.

In the episode where Nene started really being catty, and making up a romance story about herself and Kyo, Guchuko seemed to be able to understand it well enough to start tearing up as Nene related Kyo's dramatic death scene. Though it's hard to tell why Gucho reacted the way she did when a live and healthy Kyo walked up a moment later... she couldn't have thought Nene's story was the truth, could she?

Given that, it probably wouldn't be hard to convince Gucho to help out at the fair, instead of leaving slaughtered goats in the front yard. Kyo probably made the maid suit herself, left it bundled up by Gucho's tree, and attached a note inviting her to the festival, probably ending with, "If you don't want to come, that's okay, but if you'd like to join in, just come to the school wearing the maid suit, and we'll eat and have fun together!" I doubt Gucho would refuse; she may be angry and dangerous, but she doesn't seem to be the arrogant sort, and is pretty clearly a lot more lonely than she would ever admit.

I don't think there's any doubt that Guchuko understands spoken Japanese, but I doubt she can read it, so a note would be pretty useless. But Kyo could explain it to her, or maybe show her a picture along with the costume.

Anyway, I like that image. Guchuko is just entirely too cool.