@Lisahey Touché. Sex ed for women in that social setting at that time would probably be along the lines of (dramatic noble voice) "you must provide your lord husband with an heir. This is how you will do it", etc.
Then again, since the samurai in question, iirc, doesn't seem to be an heir to anything too significant (his
older brother was the one he got in a fight in one of the chapters), maybe the wife's parents and the samurai himself thought it wasn't that urgent?
That aside, I still do find it pretty funny. To each their own; it'll get better soon, I'm sure.