@ruc38 This is a tough one that I've also faced in the workplace. Here are a few things that I considered at the time and might be helpful to you.

Was the manager already in this position when you came to the agency 3 years ago? Is there a possibility that your manager will retire anytime soon, move to another position or to another agency? Do you have any inkling that your manager is trying to get you to resign by ignoring the good ratings you get from your patients and "cherry picking" only the few negative ones. By doing this do you think she might be trying to get you to leave the agency?

In my case there were two layers of managers who were intent on trying to get me to resign. It was a power play and really had nothing to do with me but it made me miserable. I was in the way. I did start looking for another position however both of these managers retired and left the workplace within a few years after all of this began. I'm retired now and their behavior stuck with me all the years I remained working and still bothers me now. I was the same age as you when all of this happened.

You could start looking for another position. It gives you options in your life. I looked for other positions and nothing came about at the time. Had I received a good offer at the time I would have taken it and left. But that's me.

I agree with @edsutton that talking with a life coach or therapist could help you to deal with the stress and decide what you'd like to do. If your agency as an EAP (Employee Assistance Program) you could book a few sessions and the bonus is you won't have to pay for the sessions. These sessions are meant to be confidential, short-term counseling, and confidential.

What do you think you might do next?