She's hoping for one that preserves the Apple keyboard layout.
That is why there is the setting in System Preferences > Keyboard & Mouse > Keyboard (tab) > Modifier Keys… (button) You can adjust the modifier keys so they are where you want them no matter what the default labels. I think any modern USB keyboard really will work for you. How portable are you looking for? Some roll up and will fit in a pocket, but they are not so easy to type on. Are you looking for Blue Tooth to save the trouble of cabling? If you want to get by on the cheap, I suggest the early G3 iMac keyboards, which I am pretty sure are not being manufactured nowadays. But they are true Apple branded and durable, lay flat for travel, and two inches less wide than contemporary Apple keyboards.
