Well I have an update - after tiring of not being able to read my ebooks (due to said wife taking reader) I went out a couple of days ago and bought her a Kobo wireless. Great screen, plenty of room for her books. I've mentioned elsewhere that it's great for people like her who have carpal tunnel issues in the wrists, as she finds it very difficult to hold a DTB open for periods of time. The size/weight of the reader is absolutely ideal, and alslo loves the font scaling too (preferring a larger font).
Plus I get my reader back - and remove all her books from it too!