She knows full well you've received it. She wants a response, but probably knows she isn't going to get one. I sent something along the lines of that message years after breaking up with my ex. It's a self closure/trying to forgive whatever actions that drove her over the wall.

In a way I'm glad that my ex never responded. In hind sight, it wouldn't have been healthy if that can of worms was opened again. Stay healthy. It's better for the both of you in the long run.