I think an inbox and outbox would be helpful for dmom. Then I could tell her (or myself, as the case may be) if the inbox starts to fill up past the edge (1" or so, I'd say) then that stack HAS TO BE taken care of. The outbox would just corral the outgoing mail, of course, and I would be taking care of that on the same day I did it... but if she got to the point that she could manage some of this on her own, it would give her a place to leave stuff for me to mail. (She does not like to put financial things in her rural mailbox for some reason, and I use a post office box, so I'm at the post office every day. No problem for me to drop off out-going mail there.)
I'd get rid of couches and chairs before I'd get rid of my desk!