1. Hysterectomy is a surgical method, not a diagnose. In ovarian cancer it would be the wrong surgical method because it is the removal of the uterus, not of the ovar, which has to be removed together with surrounding lymph nodes in ovarian cancer.. Hysterectomy can have some other cancer as reason but also myoma, which are non malignant, descending uterus, dilatation (e.g. after the 10th delivery) and many more other reasons. It is therefore very likely that your mother doesn't have ovarian cancer at all and more likely that you also don't have it. In the age of 17 it would be a (negative) miracle. Nearly all patients are in the late 30s, early 40s, which doesn't make anything better.
2. Chances: Ovarian cancer is the most ugly and nasty cancer on this planet.. Depending on the definition of "survival" it might look optimistic that in literature 50% of the patients survive the first 5 years after diagnose. In real life the chances are zero. Therapy can only extend life for a little bit of time.