Her concern is quality of life for the time she has left.

I'd feel the same way if I were in her shoes.

My biggest concern right now is that I'm observing what I believe strongly is depression.

That's normal.  Her doc could prescribe an antidepressant, but there are other ways of dealing with depression.  If you don't have it, you might want to read On Death and Dying by Elisabeth Kubler-Ross.

Perhaps your mother would just like to spend some time talking to you about how she feels.  You might also try to find out what she'd like to do in her last months or years.  I think about this every time I have to go to the hospital with cancer or another disease.  The other night on TV (commercial?) someone asked, "What would you do if you knew you had six months to live?"  Immediately, my husband said that if we knew that, we'd have to pack a lot of travel into that time.  My response was that he would be going alone, because that is not what I would want to do.  Different people want to spend their time differently.

Are there things you could do with her that she would consider fun?  Little day trips or lunches?

Does your mother have old family photos or photo albums or family memorabilia?  If so, you could go through those with her and get her to talk about them.  Write it down!  That is one of my regrets.  Now I'm left trying to remember what she told me and trying to figure out a lot.  More than anything, she might like to talk about the people and places and the events that were captured in those photos.  In addition, she might enjoy thinking of them rather than dying.

She had a mouse in her apartment which she claims wasn't removed by maintenance for two days and this morning seems to not be able to handle anything.

I would freak out if there were a mouse in my apartment too!  Especially on top of her health problems.  She doesn't need to deal with a mouse right now.

This is going to be hard on you as well as her.  Be sure to take care of yourself