I'm not sure I understand where you need a smaller device. I'm assuming not at home since then there is no storage/transport issue. I'm also assuming not at work since that would be unethical and in some cases illegal.
When I'm away from home I'm traveling by car, train, or airplane. Trips by car often do not involve luggage but I'm in my car so I have the glove compartment.
Trips by train or airplane always involve luggage of some sort even if it is just a briefcase. In which case the kindle is in the luggage.
Where are you frequently going with no luggage and no car that allows you plenty of time to read?
UPDATE: Also, what is wrong with these?
You could get her the Kindle app for her laptop, and then send her to Manybooks to pick out some free books to read. The Kindle app lets you dim the background color on a page of text so it doesn't burn your eyeballs out when you're reading ebooks.
You can re-download your purchases to another Kindle of yours (or a registered app). Even if you delete a book, it is archived online in your account.