Giving anyone who claims to be possessed by a demon control of the rules and membership of any forum is a bad idea. Let's consider three scenarios:
1. If she is in fact possessed, you're giving over control of a forum to a person possessed by a demon.
2. If she is not possessed and thinks she is, you're giving over control a forum to a person with intense psychological delusions who thinks she is possessed by an evil spirit and capable of anything.
3. If she is not possessed and knows she's not but says she is, you're giving over control of a forum to someone who is lying, probably to mess with us.
Apart from the specific individual given control, there are other issues here. I don't think it's wise for an Internet web site to be getting involved in dealing with the occult. Seriously, leave it to the professionals. These folks are in need of a priest or a doctor, not a bunch of amateur Internet religious commentators who post to message forums as a hobby.
It is hubris to assume we're qualified to deal with this sort of thing. If folks need help recovering from something like this, they should see a priest, a psychologist, a real-life supervised support group -- maybe all of the above. We're going to make things worse rather than better more often than not with this sort of concept.
Moreover, it's inevitably going to attract folks trying to draw people into the occult and so forth. I'm not always sure what I think about religion and Christianity, and heaven and hell, and so forth; but I can tell you this: If demons are out there and possessing people and this poster is what she claims, I would highly suspect Erwin was tricked into creating this forum for the demon's own ends. What do demons and Satan do in scripture? They lie and manipulate good people to bad ends. Something to consider.
It's best for the site as a whole just to stay away from this stuff. It's not a mission for an Internet site.