Ah the sh**ty co-worker.

The only thing I can tell you is avoid her as much as possible and don't bother fighting with her unless she attacks your job directly. Review your job description and make sure it's up to date. If there is a direct report tree make sure you are clear on this and ask that it be updated if it's not clear who you report too. Save all emails, memos or anything written.

If she really is this chaotic and trouble making, she will eventually hang herself without your help.

Try to continue doing the things you can do that relax you. You have been there for 15 years as you said. You will probably outlast her.