RacePhoto; You can get GIMP for Mac too. No need for neither Windows nor Linux. But she might as well try to learn PS as learn GIMP, in my opinion. And that's out of the question for the moment. iPhoto is quite good but doesn't have enough twaeking options and can't add borders nor text (I might be mistaken as I haven't used it myself in ages).
Found something called PhotoComplete which seems quite brilliant for a software novice. And combined with iWatermark my mum's now quite happy. Thinking about introducing her to LightZone once she get's the hang of curves and a few other things.
Thanks for your suggestions, guys, but the problem is now solved
)