Had a long affair with a married woman, could the child be mine?

I had established a friendship with a married lady I worked with, eventually it became an affair which lasted a few years. One of the problems was that her husband seemed to ignore her. She had said that they did not have sex or even sleep in bed together. At the end of our relationship, she had told me that she was pregnant, saying it was not mine. I was upset as she continuously told me they never slept together. The most recent time before she found out she was pregnant that we had sex was 4 weeks, she said that she had sex with her husband 3 weeks prior and that it had to be his due to the timeframe. We had an argument, and she claimed it was the only time. That did make me realize what I was doing though, so I backed off. I have not spoken to her since, but still wonder if the child could be mine. If I were to see the child there would be certain features that would make it obvious as none of her family or his have native american blood and so certain traits may show, who knows though. I am just wondering what the possibility is of it being mine, whether or not she wants it to be. I don't plan to bother her unless she wishes to speak with me.