Wondering how to be positive at work

The last couple days I've been really struggling with dwelling on anxiety, anger and stressful feelings. Usually in regards to a coworker. We rarely see eye-to-eye, and the last several months she has been completely negative. In fact it's been affecting all of us around her. Most of the time, I've been able to separate myself from her negative comments about anything and everything.

However, these last few days, I have a hard time falling asleep and then staying asleep, and when I'm awake I keep coming back to her. Ugh! I just haven't figured out how to move forward as positively as possible.

Sometimes I feel sorry for her that all she has to say is negative.