I do sympathise with your predicament and i know how difficult it can be. I use an Olympus device in my work that I bought in Maplin and looking at their website, they have a fairly simple recorder with big buttons that might well suit your partner. Here's the link:
http://www.maplin.co.uk/p/olympus-dp-211-2gb-voice-recorder-a57lk
It's a lot cheaper than the usual Olympus devices. It seems the more facilities there are on these things, the more expensive they become and the smaller the buttons are. It may be worthwhile Googling the model number to see if it's available cheaper elsewhere.