I assume your mom doesn't already own lenses from either Canon or Nikon, so that shouldn't be an issue.
I have a 5D (original) and love it. I have no experience with the Nikon D7000. However, there are some differences that bear considering:
In case she has any interest in video, be aware that the D7000 does video but the original 5D does not (the 5D Mk II does).
I upgraded from a cropped-sensor Canon 10D to the full-frame 5D mainly because the viewfinder in the crop-framed 10D was too small (a little like looking down a long tunnel). The D7000 has a DX-sized sensor, less than full-frame, so do look through the finders of both and see if the difference matters to your mom.
The D7000 is newer technology and has better weather- and dust-sealing than the 5D.
The D7000 has a few more megapixels and probably has better dynamic range and noise characteristics -- I don't know.
It would be good for your mom to hold each one, look through the finder, and try the controls for normal shooting. If one feels better than the other, that should be a very important consideration, IMHO.
I hope this helps a little, and I hope someone who has tried both will chime in hear.
Eric