Ok, assuming the max she wants to spend is 2000 then what would be the best, idk if she does but I told her it may last longer to get the better one...
On the Apple certified refurbished store, they have a 2013 iMac 27 with 1TB Fusion Drive, 8GB RAM for $1949. Something like this would work well for her:
http://store.apple.com/us/browse/home/specialdeals/mac/imac/27
For professional photography I'd suggest getting a screen calibrator if she doesn't already have one. E.g, Color Munki: http://www.bhphotovideo.com/c/product/798928-REG/X_Rite_CMUNDIS_ColorMunki_Display.html