I think I'm going to confiscate my daughter's sketchbook from what I saw in it.
Why would you want to confiscate your daughter's sketchbook?
There are some drawings in there that are inappropriate for her age.
I'm sure you don't want to take your daughter's sketchbook but if there's inappropriate material in it then you should take it away. As a parent you have the right to decide what your children should see. Explain the situation to her and help her to understand why you're taking the sketchbook away.
She's been drawing for 3 years now. She should know that she's not allowed to draw nudes. She's going to learn to stop.
I guess it depends on her age and if she's in a professional or school art class. Drawing nudity like pornography is definitely not okay, and you are a good parent for trying to set boundaries. She is a wonderful artist, but I think it's best to let her focus on other drawings until she's older.