The horse accepts you because it views you as part of its pack. It believes you are no longer a threat or a foreigner to its pack and doesn't have a reason to run away from you. The acceptance is a great thing but the type of acceptance is another.
If she is pushing you around and getting in your space you will need to correct her quickly. While she may have accepted you she assumes your just another horse she can dominate. This can be dangerous if she can do whatever she wants that will lead to all types of dominating and "sassy" behaviors.
My horse got the name "Sass" because of her attitude! She never accepted the previous owners as dominant and seemed to display a sense of stubbornness despite winning a couple of awards. After she made her very first jump with me she bonded. I could see subtle changes in her a few months beforehand such as changing of ears direction, a more relaxed body posture, and not moving away from me when getting her out of the field.