The focusing capabilities are dependent on the lens. What lenses does she have? The resolution isn't that important unless you're shooting pics for posters. My suggestion is have her sell her lenses, keep rhe D3000, and just add your budget once she sells her lenses and get the 24-70.
Here are my sample shots with that lens
https://www.flickr.com/photos/happyd300/
Here are my sample shots with that lens
https://www.flickr.com/photos/happyd300/