I sympathise. I have tried this half-way method:
Decide how much time you can realistically give her.
Write down for her that you will be visiting 2-5pm on 30th October to help arrange anything she needs. Put this in a prominent place.
Contact her kids and tell them that.
Whilst there, obviusly sort out all the bits and say 'what is happening in the next 2 weeks that you might need help with?' so you are on top of things.
Contact kids 'I have seen your mum today, have done XYZ. I will next be visiting on.......Before that, you need to check that she has ordered repeat medication (or whatever, make sure you give them at least one little task)
A couple of days before next visit contact them again 'I am going to see your mum, I will check on XYZ, have you sorted ABC?'
I am sure that as a nurse, you are very aware of this, but I know that when we're in the middle of something, it's difficut to see the wood for the trees. Although it keeps you somewhat involved, it helps with boundaries. Then once the pattern is established, you say 'I won't be able to call for a month' or something similar.
Good luck!