Thank you so much @socent for taking the time to keep discussing this very important topic that isn't discussed enough and is very misunderstood.
To start, I would say that all the things you listed are very important not only to someone suffering with depression, but any human being, and most importantly they would be excellent guidelines for any successful relationship.
Depression is something that can be tied to physical trauma (such as a TBI or any number of health conditions).
Depression can also be something tied to a mental condition, either something you may have lived with your whole life such as bipolar disorder or something with a later onset such as dementia.
But basically, anything that can cause depression is a physical condition because it is founded in the brain, which is a physical organ, and operates on very physical foundations: chemicals, hormones, synapses and such.
It DOESNT operate on good intentions and warm fuzzy thoughts. You can't heal depression by looking at more kitty motivational posters and watching doctor Phil. I am speaking of chronic depression here not the ups and downs that everyone goes through.
Since depression is a physical condition that is tied up with the body's physical health and well-being then it goes to say that there are many measures you can take that improve your physical health that will also improve depression.
You are correct in saying that healthy food will help a lot. So will exercise. So will human interaction (studies have shown that everyone gets healthier with human interaction and the healthiest societies in the world are those which are the most interactive).
I've worked with the elderly before and seen the full spectrum of functionality. Unfortunately they are much more susceptible to health conditions but like with everyone, as long as you are pulling breath it's never too late to try for better health.
About meds: I'm not a doctor, and this isn't medical advice, but let's say that overmedication of the elderly (as well as the young with depression) is a serious problem.
I've seen elderly people who were practically comatose go to being high functioning and getting out and about on their own every day when they (with a doctor's supervision) cut most of their meds.
I've seen the same things with fellow young combat vets who had been prescribed bucketloads of meds for every thinkable condition.
Holistic and natural is the best way to go IMO before seeking medicated alternatives.
My grandma is in her 90s, lives alone, and has had several surgeries. She would seem the prime candidate for depression, but she is extremely high functioning. However it's a full time job for her.
She gets out and interacts with friends every day, goes to the local rec center and does swim aerobics several times a day edit "week", and with my encouragement has got off of the narcotics that she was prescribed for chronic pain and is instead treating them by keeping active and strong so that her body supports itself better, eating healthy, and using lower risk alternatives for pain such as NSAIDs, ice and heat, stretching, and elevation.
It may sound cruel trying to keep the pain meds away from my grandma, but when they turn her into a constipated, dizzy, forgetful individual who suddenly is nonfunctional and depressed you can judge for yourself what the better kindness is.
You are so lucky to have supportive friends and your friends are so lucky to have a friend who is so in touch with herself and courageous enough to take charge of such difficult topics.