I took my present position while in the process of recovering from a brain injury/stroke.
My position is well below my abilities but I took it because I needed a low stress environment, and stayed because I like the place and the people.
My problem came in after we were purchased and went through, duties shifted, and I had to take on more work. No problem, I'm recovered and can take on more.
The problem emerged when a coworker, who had been with the company 15 years longer than I, noticed that I have much more knowledge and skill than she thought.
Now, I have someone far more senior than I constantly asking me for advice on how to do HER job, asking me for technical solutions to her problems, and asking me about how to write her documents. The worst part is that I have to repeat myself five times for the point to sink in. Other coworkers hear me raising my voice when I get frustrated with her, and it's making her look bad. Edited to add: Yes, her, not me. People are familiar with the frustrations I've outlined. I rarely raise my voice, and people have asked me what she did.
She sits near me at work, with the COVID plans, she's the closest one to me. She will also call me when she is working from home and is a terrible gossip.
How to I tell my coworker to back off in a professional manner"
I ended up escalating this to my boss. It turns out that this had been an ongoing problem with multiple complaints. My coworker has been let go.