g4 and mini are made to compete with each other. benefits and drawbacks to each. fanboy's of each are going to say their's is better, but we are honestly talking about fractions of a percent, considering what you can find in the next price range. the axe is basically MINI (part 2) and was better than the G4. the new G5 is made to compete with the axe, and my predictions come true, will be better than the axe as far as statistics go.
If you bring it down to that choice, take her to the store, and let her hold both and play around and decide which one feels better.
but as much as I can hate on the mini because it looks gay in my opinion, I know its a fair and decent marker, and I would be a fool to lie. that being said, I bet you can find a nice used upgraded mini here, easier than you could any G4. but you do have experience with the G4, so it could be a good choice.