It is very difficult to help someone who is resistant to treatment. You cannot force them to do something that they don’t want to do. The only time you can force a person into treatment is when they are a danger to themselves or to others. Short of that, there are limited options.
Try suggesting to your mother that she see a psychotherapist instead of a psychiatrist. This doesn’t mean that she should avoid psychiatrists but that she might be willing to try a new approach. She has tried a multitude of medications and has had very little success. Maybe psychotherapy would help her.
Seeing a therapist is a very different experience than seeing a psychiatrist. Many psychiatrists do not provide talk therapy. They tend to focus on medication. Psychotherapists, on the other hand, focus entirely on talk therapy. Psychotherapy can be quite an effective treatment, especially when it is combined with psychiatric medication. If she tries a new treatment approach, it might help to decrease her depression.
You might want to also suggest group therapy. Many local community mental health centers have group therapy sessions at very affordable rates. Some groups might even be free. Many people find that group therapy is a very effective approach to treating depression.
If your mother is not interested in any kind of treatment, then realize you have done all that you can. As mentioned above, you can’t force someone into treatment. I understand that it is difficult to watch a loved one suffer but unfortunately you are limited in how you can affect this situation. Ultimately, whether or not she wants to treat her depression is her choice. Hopefully, for her sake and for the sake of those who care about her, she chooses treatment. I wish you the best. Please take care.