While it is nice if your horse comes when called, it is more important that you will be able to approach and catch/halter your horse without her running away. We would recommend building rapport with your mare by approaching her in the pasture several times a day, haltering her, and then giving her a treat, spraying with fly spray, leading her in for dinner, or whatever other task you need to do. Then, ending on a positive note, turn the mare loose. You can then begin to approach without going all the way to the horse, call her name, and ask her to come to you. Be careful not to give too many treats, however, as you don't want your horse always to expect something. This can lead to poor behavior such as biting. Here is the link to some educational videos on catching and working with your horse on the ground.