My Dad had Graves disease, cost him his thyroid, 50 odd years later and all's well. When my thyroid played up it was natural to blame Dad, but it was dear old Mum that I inherited my issues from. result was the same, no thyroid and thyroxine for the rest of my life.
Your endocrine specialist will ensure all goes well, there may well be alternatives to surgery. Now it has been diagnosed all those little niggles over the last months will fall into place, be assured it hasn't popped up in the last fortnight, just presented some diagnosable symptoms.
Prognosis is that she will be around for years to come to make your life a misery/bliss. (delete whichever is not applicable)