First things first, treatment is way way better than when your grandmother was diagnosed. We have lots of off label meds and even now have an on label lupus medication. I was diagnosed at just before my 22nd birthday, I'm 38 now and I'm doing great. You can get through this. It gets better.

One thing you are going to have to learn is your new limits. Chances are you've already experienced what it's like to exceed them, but now you know why. Stay out of the sun, take vitamin D, when your body demands rest, listen. Get a consistent sleep schedule and stick to it. If you are not already off alcohol it's worth considering but not necessary (depending on your meds.) Cannabis is also worth considering, but again between you and your doctor(s).

Listen to your doctor(s). Make sure you keep up with your Rheumatologist and your GP. You may have to add in an opthalmologist depending on your meds as well (don't worry about that, eye complications are rare). It may take time to find the medications that work for you, be patient. It's probably not going to be just one medication, most people do best on combinations. Be sure to get off Prednisone as soon as you can tolerate, it's only meant to be temporary and it can have long lasting effects. Find a local support group, the lupus society has them all over. https://www.lupus.org/

Feel free to DM me or add me as a friend. This isn't the end of your life, but it is the start of a big change.

This is all less medical advice than it is lessons I learned the hard way.