I’ve had my mare over 15 years and she is still girthy. Had her vet checked and solved the problem by just giving her something to munch on while we saddle her. Sometimes I just scold her and she stops. There are times when nothing bothers her. Then there are times when I go to buckle up the chest on her blanket. That ended with a back hand (not hard) just to let her know I meant business, which solved that problem. Sometimes they just need to know who is in charge.