Should I spank her?

I wouldn't. You're right it's normal to be curious. I would explain to her that it is inappropriate to show that to people and to ask to see it. That that's private and only mommy, daddy and your Dr should see that. Save the you'll show it to somebody someday bit for an older age. If you spank her for this you're telling her that's it's wrong to ask questions. Like I said you just need to make it very clear that you don't do that at school or to your friends. However if the behavior continues then I would give a thought to some repercussions. The 2nd and 3rd offense will be intentional and then it is behavior that needs to be rectified. Good luck