@suzieflynn, I have no medical background or training but I'm not sure anyone can tell you what's going to happen because the prognosis varies depending on a person’s symptoms. You can find more information here:

Stiff Person Syndrome: Outlook / Prognosis:
-- https://my.clevelandclinic.org/health/articles/6076-stiff-person-syndrome/outlook--prognosis

Here is another patient story that you may find helpful -- Sharing Mayo Clinic: Diagnosed with stiff-person syndrome:
-- https://newsnetwork.mayoclinic.org/discussion/sharing-mayo-clinic-diagnosed-with-stiff-person-syndrome/