I haven't visited this thread for a while but as an update, and with thanks to Guy Etchells who visited the archives and found a wealth of information for me, I can give a conclusion to my original question. It would appear that my great great grandmother was in there for the reason that she was mentally unstable. She had delusions and believed that two of her children were replaced at birth by cats and planned to kill them. Given that one of these children was probably my great grandfather George, I can only be thankful she was foiled. Indeed she was deemed so dangerous that the Procurator Fiscal forbade her release without his say so.
This also clears up the little mystery that of my grandparents five daughters, none were given her name.
Apparently she was in Morningside before Larbert so I think that will be my next stop.
Thanks to all who helped and especially to Guy for his fantastic digging for me.