I just bought my first horse. A 10 yo tb mare. I brought her to my place about 3 weeks ago. She was a dream...super sweet. Until a few days ago. She has now started trying to nip me when I groom her and challenges me by refusing to lunge. Her overall attitude has turned sour. I know she's testing me, but I'm not sure exactly how to handle her in a positive, respect-building way. Does anyone have some advice? Thanks!