A threat to shoot you is a terroristic threat and she can be charged with it. Next time she does ANYTHING - threaten you physically or verbally, touch you, come on your property - anything - call the police. Keep calling the police until charges result.
A restraining order is not much help. It just requires the payment of money by the restrained party, which can be taken if the order is violated. You get these through the justice of the peace courts in Houston. You may be thinking of a protective order, but you do not yet qualify for one. You must be the victim of an assault. If this does happen, the prosecutors' office will handle the protective order for you.
If you have a video camera, record her actions. If she calls you on the phone or texts you, save the messages.