Getting no responses from professor I decided to pursue a PhD degree after a few years in industry, so I contacted a professor from the university where I had received my Diploma a few years back. We had some conversations, she was rather positive as I had good grades and I used to attend her lectures.  I could not apply officially yet, since the PhD applications start during summer. As coronavirus came, we all stopped going to the lab.
I emailed the professor about 10 days ago about how to proceed. However, I did not get any answer. Is it possible that she changed her mind about having me work in the team as a PhD candidate, since we had no communication for around 1 month?
This is an unprecedented time in academia, and your best course of action is probably to just wait awhile for your professor to catch up on his emails. 

As a professor myself, I have several emails left over from the just-ended spring term that I need to respond to.  My college announced that there will be cuts to staff, which haven't been finalized yet, so it's possible I won't even be employed here next term.  My kids' school and daycare are closed, so on top of childcare I might have a couple of  hours each day to do work-related things.  And I don't run skype anymore since discovering other, better options, so if anyone in my old skype contact list is contacting me, I wouldn't know about it. 

In other words, if your professor's work-life situation is anything like mine (and many, many of my colleagues at other institutions, judging by their social media posts), he just hasn't gotten around to your email yet.  It doesn't have any bearing whatsoever on his thoughts about your graduate application.  You've got until July for applications, so give him another week and then try emailing him again with a polite "just in case you missed this" nudge--that usually does the trick.