Don't know if I can help you, but I just wanted to let you know that DS12 used to do that when he was 10. He mostly did it during class time, which his teacher felt the need to inform me of often, as if it were some huge offence. My DS has always been a very tactile kid and very curious about the inner workings of anything mechanical. Also, I think he finds some relaxation in mindlessly taking things apart. Personally, I think it's a fine trait that helps him to learn about the mechanics of the world, so our problem was not so much that he was doing it but that he was doing in an inappropriate place.
So, I don't think think that your DD taking apart the pens is, in and of itself, a bad thing. She's learning all about the pen and the mechanics of such things. And, she may in fact be doing it mindlessly. The bad thing, I think you're saying, is that she's ruining your pens! Perhaps take advantage of the school supply sales and buy her a package or two of some cheap pens that she is allowed to take apart to her hearts content (outside, if you're worried about the mess or if you just want to make it more inconvenient for her to do). Giving her permission to do it may just make her lose her desire to do it. And if she doesn't break the habit anytime soon, at least you're not out nice pens.
Good luck!
