I would definitely speak to ICO – they were amazing at talking me through a similar situation. Anyone over I believe 12 years old who has mental capacity has the right to agree or disagree to their notes being released to a guardian.
I would also clarify what notes/ information she wants – you don’t want to be copying and sending additional information that they don’t want or already have ( you are unable to charge for it)
Also need to know in what format they want it – paper versus electronic (although again if you can justify why you are sending it in a different format then that is okay – again discuss with ICO)
You do need to respond within a short period of time (about a month) even if it is to say the request is unreasonable- check ICO website for what is deemed unreasonable
