Okay, I've worked this one out. I think Mary is basically suffering from a kind of continued in-built desire for rebellion and child-like fantasy, away from a probable stifled Catholic childhood. Wasn't her father an ex-priest and her mother an ex-nun? Kind of explains a few things after watching tonight's bonkers-ness... She is still very bright and articulate, just a bit kooky and suffering from a previous repression which manifests and releases itself through things like this weird witch party and consequent behaviour...
Anyway, I would like to formally announce that I have moved onto Saskia as my house mate of choice, who I think really is the most normal and well rounded of the bunch....not to mention damn fit!