pokerfaced said: you know she wanted it because there's no lock and she could have escaped easily
It actually is locked. If you look at the hinges between the pieces of the wood, you'll notice that the part of it is turned, which makes it impossible to get off unless you turn it back. Since her hands can't move, she was trapped and couldn't get out even if she wanted to.
Untagged 'stockade' as this is a pillory, not stocks, and is definitely not a stockade. (a fortification or enclosure made of upright timbers or posts.)