Don't they put the name of the person on the money? Or maybe she just didn't bother to read it.
I think the joke layer there is that Futo has completely forgotten what Miko looked like when s/he was alive, even though they knew each other well then.
How should I put this...Look at this...Very charming whiskers in this portrait...Moiiiin#1214 Charming WhiskersCould it be that's your type?Crown Prince, Crown Prince!!Smiley face!!!TadaaahOh, come now, Crown Prince. Is it not just some guy with a tiny, unsightly mustache?