You never need to apologize for "ranting". It is totally acceptable here. I just want to say that, one of the most important things that those of us with Lupus need is an understanding and caring significant other!
Yes, when we are very ill and in pain, it is difficult for us to be sociable and/or loving. She is correct, in one sense, that there is not much that you can do to take away her pain. What you can do is understand her illness and give her that "understanding" when she needs it.
Sometimes, all we need is for our loved-ones to believe how debilitating our illness is and to allow us to do what we need to do in order to manage this disease. You are a very perceptive young man in that you understood how your "smothering" had the opposite affect on her. I am impressed by your willingness to learn as much as you can about her illness so that you can give her the type of help that she needs. It is, therefore, equally important that you have an understanding of her medications and how they can also affect her.
It is not uncommon for lupus patients to suffer from extreme depression. The depression is both clinical and emotional. This is another aspect of her disease that you should be aware of and try to understand. Lupus causes many chemical changes in the body whose imbalance can cause depression. Also, the complete change of lifestyle and the many restrictions caused by this disease causes emotional depression. It might be helpful if you support her in making those lifestyle changes easier for her. Do not insist that she try to do things that you feel will make her happy. Learn, from her, what things she feels that she needs to make things easier for her. Do that by just simply listening to her. Don't try to offer ways to "fix it" or "make it better", just listen intently and then try to do those things that she says that she needs. When you ask her how she feels and she tells you, don't try to offer ways for her to feel better, tell her that you understand how the pain can make her feel and/or how frustrating things must be. Then let her know that you are there for her to give her comfort, understanding and any help that she needs because you truly believe everything that she tells you about her symptoms and how this disease affects her. You might even suggest that she come here to this site so that she can freely express her feelings, learn more about Lupus, and belong to a community of people who also only want to help her.
She is very lucky to have you and you are a very astute and caring young man. I'm glad that you have not given up on her and I'm sure that you never will. Be patient, be supportive, be understanding and keep loving her. I wish you both the very best.
Peace and Blessings
Look For The Good and Praise It!