According to Jack Stimson's records, Mathilda was once a member of the Theosophical Society. This fact was just one of what he called the "right credentials" to be a kindred spirit — or, as Jessica Willamy put it, a "one of us" — in the counterculture movement of the 1960s. (PROSE: Wonderland)
Behind the scenes
Author Mark Chadbourn pours a lot of research into even the smallest of passages within Wonderland. Thus the fact that he describes Mathidlda as being a former member of the Theosophical Society — and current friend of Krishnamurti — is significant, at least when viewed through the dangerous lens of real world history. It seems to imply that she had turned her back on the Theosophical Society just like her friend — but of course the DWU could be different from the real world.