Obviously its leadership issues in that you aren't leading her and she knows it. There are many many ways to address this. If (and its all relative) she is truly a very dominant horse, then I wouldnt want to encourage you to try and dominate her physically in a round pen or online.
If she is food motivated then theres your place to start.
If a horse is disrespectful around food or dominant then this is what I do. I don't know if you stable her, but if you do then offer her some food in a feed bucket. Personally I open the door and stand there a few feet back (out of strike range) They have to offer me both ears, upright, focussed on me with no sign of agression. One ear isnt enough. One ear and a hard eye isnt enough. If they step forward I move them back. They do not cross that threshold. They get the food the SECOND they offer two ears and soft eyes with no disrespectful signs or impatience. Even with horses that are fine that remains the cue - its just a daily tune up lets say. If you need to have a stick or whip in your hand tap them on the chest (make sure you are out of the front strike zone) or even use one of those door chain things at first if you need to.
Another very powerful way to set rules is to take feed to the field. Put it down and keep them away from it. You are claiming it. You control it. If she approaches ask her to stop in her tracks. If she doesnt - chase her away however you need to. Take a long rope and whirl it, throw it, bags on sticks anything you personally need to keep a safe distance but make her move. Then go back to the bucket. Keep repeating until she stops when you ask, and offers the same passive expression as described above. Then you can invite her in to the food and move away.
Control over food is a very powerful way to establish dominance, as well as establishing your space, and the beginnings of communication, and her having to take notice of you, without needing to physically fight with her.