Sorry, I wan't suggesting that she should buy a Leica. As I said, as an anecdote, I was amazed at the difference in the sharpness of the images with the Leica.
As for what to buy, great photographs can be taken with any camera. If you have a Minolta and like it, great. The reason most people like say Nikon and Canon over most others, is due to their systems. All the lenses accessories etc that are available for them. The top of the line ones, usually considered "pro" cameras is possibly due to the more rugged nature of their parts. Not sure but that would be something that an amateur probably doesn't need to worry about.
The other consideration is that with Nikon and Canon you will probably find it easier to rent lenses at rental outlets. Speaking of rentals, buying long lenses like 300 and up is often not necessary when you can rent them for a weekend for pretty good prices. Unless all you shoot is birds or nature, or fashion, then buying may make more sense.