This sounds like a disaster waiting to happen. A mini loose in a field (thinking spring grass and the possibility of founder) wearing a halter around her neck that she could get herself caught up in and you can't catch her? Is she at your house or the previous owners? If she is at your house you had to have had your hands on her at some time.
Do you have another horse or is there one close by that a neighbor could bring over. Thinking maybe she would come to another horse.
You said she would come to a feed bucket. If she is eating out of the bucket can you get ahold of the halter?
Can you get her into a barn or stall and block her exit?
Do you know anyone with roping skills?
She absolutely needs a much smaller space until you can get her accepting of being caught and handled. You do have a project!
Wishing you the best with this girl. Hopefully someone here will have the perfect solution for you.
Welcome to the forum.
If you ever find yourself in a fair fight, it's because your tactics suck. ~ Marine 1SGT J. Reifinger