There is a woman I work with who I used to be friends with. Now she's not speaking to me.

I tried to text her to ask if I had upset her and she didn't reply back. I didn't want to cause drama at work, so I have simply remained polite and cordial toward her, but she is barely speaking to me. I have no idea why she is upset with me, and no idea why I let it worry me if she will not be open and communicate what the problem is.