Maybe I'm missing something but when I go to CP->Options, I see the box for selecting which forum to opt out of but no way to set it.
Just select the forum you want to skip, using ctrl+select for multiple selections and then just press the 'Save Changes' button.
I did that for the ibot girl, the only one I selected. I still got the posts from her.
You may have done something wrong, because it works fine (opting out of forums, including iBot forums).
To completely get rid of her you need to select (as of this writing):
Security Advisories (RSS)
Security Advisories (RSS) - Microsoft
UNIX and Linux RSS News
Software Releases - RSS News
Complex Event Processing RSS News
Chat with iBot - Our RSS Robot Girl
I count 6 forums, not 1.
Then that explains that.