Here's the thing: back then even classroom miscreants knew better than to label everything related to female genitalia "vagina". Women have vaginae, to be sure, but it's hard to actually see one without a speculum or internet access.
If sloppy writing bothers you, just give this book a miss. The author blogs as The Blogess and she's funny online in a way that doesn't transition smoothly into a book. The constant reminders that you're reading a book, y'all, were off-putting. The recycled blog stories lent the book a phoning-it-in air that I resented. The unrelenting use of the words "totally" and "fucking" as intensifiers, which is not too disturbing in a blog and most likely charming in person, did not enhance my page-turning experience. As you might guess, she also refers to her vagina incorrectly many times (when she does use the term correctly, it's usually regarding a hapless bovine's vagina). It might seem as if I did not enjoy the book, but these annoyances did not detract from the fact that the stories were funny. I will overlook a multitude of sins for a funny story and the book is full of them, so if I haven't scared you off by now I say go for it.