First thing is to get lupus under control and see how you are. It is possible that you will be able to handle school and a nursing career but getting lupus tamed should be the first order of business. Many women with lupus do have children. One in our support group just announced she was pregnant and doing fine (her symptoms actually decreased) and others have had children in the past.
You are in the early stages having just been diagnosed and starting treatment. Hopefully, in a year you will have a different perspective and be able to make decisions about your future without the cloud of a newly diagnosed and treated case of lupus. If you are sick enough to consider disability then I would guess it would not be good to proceed with school and the pressure and work it will bring. Stress is not good for lupus in general. I know this is a disappointment but your first priority should be your health. You are young and have time to do things and make changes in your life.
It is important to accept what has happened and define a new normal for now so that you can shape your decisions and life around your new reality. Once things are under control you can begin to make decisions to move forward as planned earlier or modified plans that fit your state of health and energy. For now try to take things one step and one day at a time. Set the long range plans aside so you can concentrate on getting better without any added stress.
Hang in there and hope your treatment works quickly.