Mediocre research career so far. Can I salvage my career by continuing as a postdoc with my PhD advisor? I made a huge mistake of working in a field different than my advisor's expertise. My PhD research was in computational modeling of 3D printing process using finite element analysis.
While my advisor's expertise is in density functional theory and molecular dynamics simulations. She works on battery research and my colleagues working on those projects get  published in &gt;15 impact factor journals.
Due to covid, I did not relocate to other place for postdoc and I have been pursuing postdoc with my PhD advisor for the past 9 months.
I have already destroyed my chances of getting an academic position by being a simulation guy in a experimental heavy research field. I am trying to find another position but failed so far. I am having an ongoing discussion about a postdoc position with another professor from another university. He will let me know if he secures a grant.
Meanwhile, my advisor has offered me one more year of postdoc position. Am I heading on to disastrous career by considering her offer?
For the past 9 months, my work has been different and I am enjoying the new learning opportunity.  But I extremely worried about my future.
Please advise.
Am I heading on to disastrous career by considering her offer?

No.  There is nothing wrong with considering and accepting a job offer from your PhD advisor, or an extension thereof.
What is disastrous for your career is not looking for a better job and taking one as soon as it is feasible to do so.