I hired a freelancer and it seems all nice and good. The task is very simple. She sends me the first samples, I reply and after a month I am still waiting for her response back. During this month I wrote several times asking if everything was ok with her.
I don't know what I should do. I want this job finishes soon without nor more delay.
Look for someone else or finish the job internally, or for another freelancer, there are various reasons why a freelancer may become unresponsive that don't necessarily reflect on them as a person, medical emergencies and the likes. Or they could be unprofessional and simply be ignoring you. In any case, waiting for someone to respond for a month for a job that likely takes less time is a clear signal to move on.
re: "I don't know what I should do. I want this job finishes soon without nor more delay."
It is not the freelancer's responsibility to ensure the your project is completed.
It is not Upwork's responsibility.
It is the project manager's responsibility,
If you didn't hire an independent project manager, then you must fulfill the role of the project manager.
None of your customers care if the original freelancer finishes this project. All they care about is that it gets done. Of course that means hire more people if necessary.