May also be you are babying her too much and being aggravating in general.
Horses as a rule don't do as well with "softly" as they do with firm.
And horses cheer up when they have a firm leader. She is trying to put you in your place, which is not as the boss of her.
If you are babying her, quit it. If you are giving treats, quit it. If you spend time talking to her, quit it. Establish yourself as leader, not the flunky here.
The more you behave as a leader, the less horse will show this attitude.
And if this is used saddle, you might need to check it again for defects as well as address your tacking mechanics, as well as riding.