How to tell if someone likes you?

I met a woman at work and we started chatting every time when I see her at my work, we went on a first date and it went well, than we went on a second date for dinner and on our second date we had a good time, chatted a bit even invited me over for coffee. She mentioned that she would like to spend one weekend with me. Than before Christmas I invited her again for coffee and she said she would come back to me (that would have been a third date) but she never did.
And on Christmas eve she send me a message wishing me Marry Christmas, I asked her if I could come over the following day but she told me she is going to visit her brother, but that was not true because I bumped in to her daughter at a mall, I called her but she is not answering her phone and she is not replying to my text messages. I don’t want to force the issue with her because she is a an introvert and she got divorced a few years ago. I like her because she is a well educated woman.