I hope somebody there will help you out, but meanwhile, let me say I too have vision problems. I had the Sony Reader, but even at their largest font in landscape mode, it was difficult for me to read. I could do it, but just barely.
I got the Kindle last January and believe me, it is wonderful. I'd hazard a guess that the three largest font sizes (out of six total) are all bigger than the Reader. I usually use the 20 point, but can also read the next lower with ease.
If you don't connect with somebody there who can show you one, I'd suggest you go ahead and order one, as Amazon's 30-day return policy is really no-strings. Your wife would know very quickly whether the type would be suitable. I'm betting it would be, but if not, just tell Amazon and you can ship it back.
If it turns out to be what she needs, then you won't have to wait anxiously to order one, it will be right there to start reading.
And I feel Amazon has many, many more books that Sony's store, and almost all are less expensive. Almost all are $9.99.
Good luck!