Now you mention it, is her horn fake as well, like Kongou's?
no mention of it in her voice lines... most likely they are real no real certainty as to why maybe because unlike Kongou who was 100% British, Mikasa's armor was made by Kruppstahl? without Criin's notes I can only imagine that Mikasa was based on Togo himself who did study in Britain for 7 years thus explains the horns
Updated
Ähm... that would be 'idle hands', though...
Chapter 012-2
Azur Lane 4Koma Manga Slow Ahead!
HoriConcentrate on cleaning! Idle hands are the devil's tools!What's this...?Ja... Jawohl!dust
dustsqueeeezeThis brings back memories.BUMPWe... Well, no helping it then. Just a little while, alright? Let every man do his utmost duty!bashfulAlright, listen—make sure to follow the lines of the tatami when you wipe it!Could you try wearing those... yes?Oohhh... those are the clothes I wore back in my heyday, are they not.