All About ?Nora?

I remember reading a books around 6 years ago, about a girl (I remember thinking her name was a bit intriguing, and not that common...all I can think of is Nora).
She was living with her dad, somewhere not in the city. It may have been a farm. Her mom had left them a few years back, and was living in the city with her new boyfriend.
Then her mom sent her a letter asking her to come stay with her.

But the most potent memory I have of the book is this one scene where she woke up early, went down to the ?river? on their farm and went skinny dipping.
But when she got out she realized she was bleeding. She panicked and asked her dad for help, and he tried to explain to her that it was her period, and then tried to explain sex by using a cake-baking metaphor.

I hope this helps XD never got to finish the book since I picked it up while waiting in a library.