Tough call, but I say seal her: she's too dangerous and volatile, and despite her sob story, she's not made much of an attempt to change her ways or get help. At this time, it's just safer to get her sealed up so that she's less of a problem.
Now, Parsee could have a bit of sympathy: she knows what it's like to be controlled by her nature. However, she had Yuugi to help begin the process of dealing with it on her own. Lumia doesn't have anyone who can help her and keep her in check, and Parsee has neither the time nor inclination to be that for her.
That said, a few things that the parser mentioned gave me a few ideas... :3 Though, I have no idea how to implement them.