I recently bought a new 3 year old mare from a good friend of mine, for a very good deal. The first few times when I went out with a halter to catch her, she would stand calmly and accept it. But, suddenly, and for no apparent reason, for the last couple weeks whenever i go out to the pen with a halter, she will take off at full tilt, and refuse to let me catch her. How can I teach her to let me catch her when I go out with a halter, so I can finally work with her?!