She is beautiful!

A pony is anything 14.2 hh and under.

Next time you groom her, do not tie her up! Hold her lead rope with one hand and groom with the other. When a horse is tied up and is frightened, they can't get away and they start to panic even more. She could injure herself or you while trying to get away.

Is she kept in a pasture or a stall? What are you planning on doing with her in the future? Is she going to be trained for you to ride or just more of a pet?

She does sound like she wasn't treated right at her old home. Just give her lots of love and carrots! Make sure that you are out there with her not just when its time to groom, etc. Go out and just sit with her, but let her come to you. Get her used to seeing you around and let her always make the first move. The one thing you don't want to do is start to build up trust and than try to rush things and all that trust is gone.

Once she trusts you, you can start to get her used to objects that she was afraid of. Let her come and sniff and touch the object with her nose. I would do that in her pasture so that she can come and see whatever it is when she wants to. If you are going to ride her someday, let her see and touch the saddle, bridle, saddle pad, etc. so she becomes familiar with it.