As I understand it, you are both in your mid-to-late twenties, way too old to behave like little kids throwing daily tantrums. You, being the older twin, take the initiative to call a truce and invite your sister to a sit-down discussion, just you and her in a quiet place. Leave all the bile and toxins elsewhere as you tell her what’s on your mind; explain that you both want the same things for the business but her approach is not constructive – case in point, the employees leaving in droves. Ultimately, this is killing the business and your relationship. Speak from your heart when you tell her that your father loved both of you and that, because her interests lay in different areas while yours were fulfilled in the business, he felt secure in having you take control. Perhaps, if you could to try to work with her in a mutually respectful capacity, she might turn out to be a great help to you and ultimately a wonderful friend and loving sister. Give it a chance.
Communication is the pathway to great achievements. I truly hope it works for you and your sister.