1. what are you going to tell the HR?
2. if she has the habit of 'bad-mouthing' most people in the company, chances are that she is famous for it. so the HR probably will know too.
3. personally, i feel that by discussing it to HR, in a way, you are 'bad-mouthing' her too, if the HR stands on her side.
if i am in your shoe, i will
1. ensure that i work on getting my work done to the bosses' satisfaction
2. work on my 'politics' with this super woman or at least avoid stepping on her toes
3. work on getting the bosses and HR to be on my side (via perfecting my work as well as getting to know them on top of on a professional level).