Here are links to some articles, from PsychCentral's archives, on the subject of how to help someone who is struggling with depression or other mental illness:

https://psychcentral.com/blog/11-way...-denial/?all=1

https://psychcentral.com/lib/helping...ression/?all=1

https://psychcentral.com/blog/how-to...essional-help/

https://psychcentral.com/lib/how-can...hos-depressed/

There is also a book I have seen recommended as a "must read", in one of PsychCentral's "Ask The Therapist" columns, for family members of people who have a mental illness but who are not willing to seek treatment. It is titled: I'm Not Sick, I Don't Need Help. (I believe it is available for purchase on Amazon.) Here's a link to a review of the book:

A review of "I'm not sick, I don't need help!" - Friends for Mental Health

I wish you both well...