Welcome Sarah,
I'm new to eReaders, Had my Sony PRS-600 just a week, and have had a problem, which will hopefully be sorted soon,
Also I am slowly loosing my Eyesight, I need Very Large Print or I just can't read, Hence the eReader,
Now for the few days I have had the PRS-600 I found it Wonderful, and using the XXL Size in Landscape Mode really helps,
The point though is not just the Reader, but the eBook format you use, as the sizes and fonts available vary, hope that doesn't make it too confusing, and take it into account when buying.
Good Luck, I'm certain an eReader will help your Daughter,
Personally I Lve the PRS-600, but if you can afford it the PRS-900 sounds great !
Check all forums here, loads of great advice and info,