Would a pituitary tumor cause hormonal harm to a woman's body where she ends up needing a hysterectomy?

No, and yes: Pituitary tumors ordinarily won't interfere with a hysterectomy, unless dangerously large and need to be addressed first. So no, it won't cause harm with reference to the hysterectomy. However pituitary tumors can cause significant problems with vision, headaches, abnormal hormone levels, etc. This is a serious but separate problem. Seek consults from neurosurgery and endocrinology.