I remember that the idea of it, both appalled and attracted me.
The Mahakala nun dedicates herself to the practice of Mahakala- that is the visualisation of the palace and surrounds of Mahakala's realm, imagining the deity, then imagining herself as the deity and then becoming the deity whilst reciting the mantra.
It is a retreat that will last for as long as the nun lives and breathes.
For as long as she lives.
A permanent retreat.
The rules of a retreat are comprehensive and proscriptive.
I don't know how proscriptive a life long Mahakala retreat is.
My first thought when I heard that Samye Ling was looking for a nun to be in permanent retreat was- this isn't right. It is true that there are practitioners who take themselves off to the mountains for years to complete a certain practice, solitary practitioners and couples, but all under instruction from their teachers because they have asked to do it.
In theory there is nothing wrong in dedicating one person to do one practice. It just doesn't fit in with my image of Milarepa or Marpa struggling and begging for permission to be taught certain practices.
Another thing that bothers me, there is usually a beginning, middle and end to a practice, and different practices to be completed; granted if Mahakala is your yidam practice then it is a life long task...but you wouldn't be expected to practice it in a dedicated location.
Samye Ling was looking for someone to fulfill a role, the house was being built.
'Real' practice, for me is closer to this account:
All apects of the body, heart and mind are involved in practice, all hopes and dreams, meanings and possibilities.
Image from: http://ganachakra.com/
As far as I know it is more usual for there to be a group of monks or nuns given the task of invoking Mahakala. There is no need for it to be one person, unless something else if going on here.
The Mahakala nun becomes in effect, a part of the building. Her place of practice is Mahakala's house, and she becomes his conduit or reason to stay.
What keeps on going around in my head is that Mahakala practice can be done by anyone who has had the correct initiations, and there are many people who have permission to practice Mahakala; asking one person to do it for their whole life time looks like creating an 'expert', but it seems closer in my imagination to a more archaic tradition: that of marrying a priestess to a god.