Join the Singapore Library.
It is for free!! They have a childrens book section with nearly 3,500 titles in epub that read on your Kobo.
As for a device for her, I'd second a cheap reader but would go for a refurbished dedicated ereader. The color readers do have a very short battery life and the moment she wants to read and has forgotten to load it, which migth be every other day with a color reader, she might loose interest in it. Also Kobos are 60$ right now at Borders and she already knows how to handle it.