Here for a friend

Context: I have a friend who suffers from fibromyalgia. I don't know much about any of her other conditions, though I know she has tried many different treatments from pain pills to injections to morphine patches and nothing has seemed to make much difference in her pain levels. I clean house for her on and off, usually once a week, partly for the cleaning aspect and partly (I feel largely) to keep her company, because I know she feels very isolated. She usually has to lie down due to pain and fatigue at some point while I'm working.
My question is related to a situation that happened recently. We talk about a lot of things, but a lot of our conversations center around therapy and doctors, and how people seem to dismiss chronic pain sufferers (including doctors) because they can't see the pain, only its effect on the person. Last time I was over there (it had been quite a while since I'd gone, life intervened for both of us), she was explaining what treatments she had undergone, how she'd had to go to a new doctor and how he didn't seem to be working out either and the reasons behind that, and she started crying. She broke down completely about her feelings of hopelessness and frustration, and how she just wanted some relief, even for a bit, from the pain.
I didn't know what to say or do. I didn't know what I could possibly say to comfort her. I know I hate it when people tell me to just think positively and keep my chin up, because my experience with depression is that it doesn't matter if I think positively, getting out of bed is still too much effort. So I sort of just continued dusting and talking to her and keeping an eye on her in case she showed signs of wanting a hug or anything. I don't know what else to do.
So my question, finally, and thank you if you read all of that, is: Is there anything I could have, or should have, done differently? Is there anything that you would like to hear in that sort of situation? I have arthritis but it's a different kind of pain than she has, and I know I can't fully relate to her experience; she knows I mean well, but I can't honestly say "I know; I understand." I want to help her however I can, and in a situation like that I know everyone is different, but I don't know how I can best do that. Any insight is appreciated, and I hope this post doesn't offend anyone; I honestly do come with best intentions.

Bless your sweet heart. I sure wish I had a friend like you. It sounds like you're doing about all you can. By listening to her, and being a shoulder to cry on, you ARE helping her. And it's ok to say "I understand" because you DO have pain -- even if your pain isn't "exactly" like hers, you still have pain, and if you ask me, pain is pain and suffering is suffering! So you DO know what she's talking about. I'm sure you have bad days too, where you really don't want to get out of bed, but you have to in order to keep moving! And I'm sure that there are times when your meds don't work too -- it's frustrating, right?

If she breaks down again, don't hesitate to put an arm around her shoulders, cause everyone likes a hug now and then -- even if you aren't "close" friends. She'll really appreciate that, I'm sure. But just by your being there, you're being very helpful to her and by listening. You're a very good friend to her --- she's lucky to have you.

God bless you -- I'm sure God will reward you some day. Take care. Hugs, Lee