Thank you for your letter. Your mom’s isolation and dependence on you is something that you will want to start managing by creating social supports for her.
If you attend to your mother’s dependence by limiting your life you will eventually simply be in orbit around her and lose yourself. I recommend finding a physician and begin with a complete physical. The physician can then make recommendations about monitoring her medicine, changing it, or making other recommendations about her physical condition that might be contributing to her depression. It will also be important to help create a social network for her. You may want to talk to your colleagues at the university counseling center to see what resources they may have for geriatric services. Your job is to help create a support network for your mom — not to be the network. The professionals at your university are likely to have contacts in the community who can help.