6 Year old mare aggressive behavior?

I bought a calmness tempered by 6-year quarter horse mare in June 2009. She was a mare sweet, it worked very well but a bit unhappy when tightening the cinch / girth. approximately 2 months after I bought her she started to act aggressive. she bites and kicks, trying to put his halter on the prairie, it is almost impossible to seat unless the rope is attached short because it will bite you. she RCA is very sensative to its field and is bad when I put her necklace breast. she doesn't like me leaving on his either. shes perfect when I'm on it and when Im leading her she respects me, people said you have to Smack her and show her who's boss, and that IM is not afraid of it and it makes her more aggressive and is very terrifying. IVE spoiled, and it just hate me. Does anyone have any suggestions?

try pets dear! btw i would get its pro forma quickly

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