If your g/f is in pain during the day, there is a good chance it doesn't magically disappear when she goes to sleep. Have you ever pulled a muscle really bad? If you have, you know the pain can keep you awake because every time you move in your sleep it hurts. That's the kind of pain I have at night. I have deep muscle pain that feels like a combination of pulled muscles and charley-horses. It kind of sucks. So to answer your question: Yes, some lupus patients have pain in their sleep.
I don't know about the moaning. She may just be so exhausted. When I get really exhausted at night I tend to mumble my words and I'm not 100% there. You'd really have to ask her about that one.
Regarding dreams: I think it's pretty normal, even with perfectly healthy people, that nightmares are more memorable. They are scary and tend to wake up us right in the middle of it. Then it's hard to go back to sleep because you keep thinking about it, therefore the next morning you remember it well. I know a lot of people, without Lupus, that rarely remember any dreams at all and if they do it's because it was so scary it was hard to forget.
Leg Numbness: Pretty common. Numbness, tingling, burning, pins & needles, etc. These are all neurological issues.
You know what I think you need to do? Make sure your g/f is keeping a journal. She should write down all of her symptoms and everyday just jot down a bit about how she felt that day. It's hard to remember to do so I try to make sure I write in mine at least every couple of days. Just so I don't forget anything and I can find any patterns.
There is just one thing that I think you need to keep in mind. This is your g/f's illness. She is going to have it for the rest of her life. She needs to learn how to manage it and you just need to learn how to be supportive in the way she goes about it. You need to be supportive but also remember that it is her body. Lupus is so different for everybody that we can only really tell you about our own experiences. We can't give you specifics about your g/f. Keep asking questions because the more you learn the better, just don't expect miracle answers.
I know this is hard for you and that you just want to help her. My husband is bound and determined to find a cure. At the same time, he respects my need for space and if I don't want to talk about something he doesn't push me. He also knows that if he gets into a "looking for a cure" mode it will most likely stress me out and exacerbate my symptoms.
So support your girlfriend but don't add stress to her situation. Figure out how she needs to deal with this chronic illness and support that.
Also, make sure your read the spoon theory. It's the only thing I have found that even comes close to describing what it's like to have lupus.