A netbook I'm familiar with, but I worry that its a dying technology, but since I've sort of eliminated the tablets that are replacing netbooks I don't know that I care if its dying.
Well, since we are talking about dying technology, I would stay away from the Chromebook as well, in her case at lease. I think you should buy something with touch going forward.
If it was me, and my budget was around $249 (Chromebook price), i'd look for a used Asus Transformer Tablet
I have seen lots of transformers with docks for around $250/$300 used.
Here are my reasons:
1)Lots of cheap or free software, which if proven useful, you can always purchase the full version cheap.
2)Has touch screen; any nice touch apps will probably be supported on this.
3)Can be used with a stylus if she wants to write on it like she did with her notebooks.
4)Has keyboard / touchpad if she wants to type
5)Very good battery life without the dock, great battery life with it.
6)She can still run Chrome, Google Apps, etc on it.
You can also substitute a different tablet /bluetooth keyboard for it, but for me I really like the transformers.