Well is she tight with her info. or was she tight with her info. before she crossed? If not then you should have dropped her before initiation. Let her try again the next year. It sounds as if there was a little beef before you all went over and discovered her sickness. Why didn't the line speak up then? Did you tell your Dean about her attitude?

Sounds as if she is breaking up your chapter. I'm not sure what your policy is on expulsion of members, but I would imagine it would have to be a far serious crime than internal fighting to kick her out completely. I honestly don't think you'll be able to kick her out, but you can continue to ignore her and strip her of her duties and responsibilities to the chapter.