What constitutes a hostile work environment?

I work at a company that was started over 35 years ago by a gentleman who still runs the company today. His spouse also works for our company and, for lack of better terms, is complete and utter hell to work with. If she doesn't like someone, she finds reasons to get them fired and I would know because I'm in HR. For some reason, I am on her chopping block. She has made several complaints to my Supervisor that I "talk too much" to other employees. I am in Human Resources so I can't really do my job effectively without talking to employees. I will say though that I have made a VERY conscious effort to not talk about personal things unless I'm on a designated break time. She is constantly stalking me in the office just to see if I'm talking and who I'm talking to. She asked me to change my work hours to directly what my supervisor works (I come in an hour earlier) and she makes complaints about me to people who are not my Supervisor. No one is willing to help me and stand up for me because they do not want they're jobs to be in jeopardy, but all involved have clearly stated to me that I have done nothing wrong. I feel like I'm being hared by her, singled-out and attacked. If I get fired or choose to leave would I have a case for a hostile work environment? I have had my doctor note in my medical file stress due to work. Thanks!