The interest in genitalia and bodily waste function is appropriate for that age range, lasting probably into 2nd or even 3rd grade. You will just need to provide continued guidance (not punishment) until she gets it or grows out of it.

The fact that she exposed herself is problematic however. Punishment isn't really a good way to address this, you don't want her to have negative associations with her body. For most children repeat reminders (think several times a day from teachers and parents) that state the rules (keeping private parts covered) will help. Dressing her in "less accessible" clothes for school may also help (pants or overalls instead of skirts or dresses). Good luck.