It was once thought that Vitamin D only regulated calcium levels and gave us strong bones. More recently they have found that if our Vitamin D levels are “optimal” it gives us strong muscles, regulates our immune system, prevents cancers, regulates gene expression and much more. There is a lot of evidence that any autoimmune disease is probably caused by Vitamin D deficiency.
So to answer your question if she is given enough Vitamin D maintaining a blood level of 50ng/ml or higher, is given the co factors that Vitamin D needs to do its job, you may see most or all of her symptoms go into remission.
Has she had her Vitamin D levels checked? Is she taking/getting Vitamin D?
You might like to read https://www.vitamindcouncil.org/blog/13980/