This thought process doesn't seem super far-fetched. In Japan at least, where it used be expected for women to stop working once they get married. Many stereotypes persist in fiction even if they're no longer as prevalent in real life.
It seems unwise for a nurse-in-training to make it through all of nursing school without being exposed to some real nasty stuff in clinical internships, but then it's fairly common for teachers to make it all the way to classrooms without anyone, themselves included, realizing they completely suck at teaching and/or running a classroom. It may be dumb, but I don't know enough about the standards of Japanese nursery schooling to say it's unrealistic. The attitude of the senior nurse in this first chapter suggests it's a common occurence for nurses to leave nursing school bright-eyed and bushy-tailed and crash out when reality sets in.