I swear I read somewhere that being on pred can make your ANA lower. That was the first thing I thought of when I read your first couple of sentences and then you confirmed that you were on it. I wish I could remember where I read it. (Darn brain fog) I'm sure someone here could lead you in the right direction.
Not to get off subject...but I don't think it is the nurse's place to tell you that SHE does not think you have SLE. It was not right for her to upset you and then not be able to give you to the dr. to answer your questions. Furthermore, most docs don't go on ANA results alone to dx SLE. I'm sorry if I am out of line, but again, I don't want you to get upset or worried when you already have enough going on. Stress is our worse enemy.
I am sorry I was not of more help and I hope you get answers soon. Please keep us posted.
Kathy aka Beauchick