Hi, It's kind that you are seeking ways to help your friend and to understand what her illness is like.
One of the most annoying things about lupus is how utterly tired you are from doing almost nothing. Your friend may need an afternoon nap or be too tired to go out to a movie. Invite her as you would normally, but don't have your feelings hurt if she sometimes declines the invitation - she might not want to say she's too tired again.
Lupus folks cannot spend much time in the sun either because it can make the aches, pains, and fatigue worse. My doctor told me it would be okay to walk from a building to the car, might be okay to be in deep shade in the late afternoon for an hour or so, and never to plan a day at the beach.
If your friend's hands hurt, she might need help opening a soft drink bottle or can or a stubborn bag of chips. Play down being helpful and make it seem like it's no big deal.
Help her other friends understand she's the same person as always and teach then what you've learned here so they can be quietly helpful, too.
I echo what has been said, treat your friend like always. She's lucky to have a good friend like you!
Peace - Barbara