Hi Michelle
I am also trying to trace where my late mother was. I have been at it for over twenty years. Kildare is unlikely to be the place because there wasn't a school there. However, there was St. Patricks Convent which could be worth a try. Generally, girls were sent to nuns along with infant age boys so I doubt that your nan would have been with the Christian Brothers.
The HSE in Dublin are obliged under the Freedom of Information Act to release info to relatives with regard to Ind. School Detentions. They give the sketchiest of info and want lots of proof from yourself before they release it. However, I do think they are your best place to start.
Children were deliberately sent to the other side of the country as it was thought it best for them to have a clean break from their relatives whatever the circumstances. Also, the Schools asked the authorities to send them children when they had spaces as they received funding per head of children. So there was no sensitivity or logic displayed with regard to distances of placements.
My mum first turns up in the courts age six in 1936 charged with begging. She is committed for ten years but actually serves twelve. No one appears in Court for her and the address she supposedly lives at has denied having her there. Mum could not remember anything before "School" and we never knew who she was or who her family were. No birth records at all. So where did she come from? Snatched from the street to make up the numbers perhaps?
Let me know if you find anything, need any help or have any questions.
Kind regards
Dee