Does your saddle fit? Has she been treated for gastric ulcers?
I have (could say had) the same problem with my barrel mare, Tequila. Only, it was just with cinching up. Me being a protective horse owner/mom, I got her tested for Gastric Ulcers twice in a month (he didn't have it). When my idiot-self found out that the saddle was fitting a tad big, I let her rest for a full 2 months before going into work again (with the exemption of groundwork). I also got her a proper fitting saddle. Turns out, she is just naturally cinchy (improper training). I worked with her so it is now just pinning her ears when getting cinched up (she used to try to bite). I also do my cinch slower than I normally do.
Additionally, does she always act like this, or is it just because 'tis the season?