Welcome to MR, taylork1, and congratulations on your new Sony.
There are thousands of free ebooks for your Sony (well, to be fair, ...for your mom's Kindle also) right here on MR. Just look up at the blue bar, click the arrow next to ebooks, and on the dropdown menu click Sony BBeB (lrf) or ePub.
There are more Sony versions than ePub right now but, members are quickly adding to the ePub library.
IMO, the ebooks on MR are much better formatted (they are beautifully hand-formatted by the dedicated members of MR and, they take pride in doing it well)
You can also "borrow" ebooks from your public library with the Sony..
Enjoy your new Sony and let us know how that Sony vs Kindle with mom goes