My mom has severe depression, as do I. I find it best if we each do our own thing.
We have a dry erase board on the fridge too, where we'll write "I love you" or "have a nice day" or "I appreciate you" or such things. Whenever the other does a chore we say thank you.
She's in treatment as am I. That helps too.
We also know when to leave each other be, like I said, we pretty much do our own thing. And when she complains (which she does a lot, lol) I sort of say "okay" or "feel better" and ignore it best I can. . She complains a lot. I don't want to be insensitive to her but I don't want to dote or encourage her either.. Idk.
Hope that helps and sorry you have to deal with it!! (: