Odd coincidence or blood relative?

Have you ever met someone who reminded you so much of someone else? In high school, I met a guidance counselor who my mother swore bore an incredible resemblance to my grandfather. My mother once worked with a woman who looked so very much like my aunt (OBM) that my mother was speechless. I once met a girl my age who also reminded me very much of that aunt and even had the same rather unusual name. I had a dear friend who was often mistaken for a girl named Jade. We never did meet Jade, but on several occasions, we had strangers strike up a conversation assuming she was that girl.

I had one such experience this weekend. I met an artist who is very similar to one of my sisters. She looks similar. Her tone of voice was often very similar. Even her attitude was very much like this sister. She's even the same age.

The thing that makes this so striking for me is that my sister is adopted. We know her birth family (she was raised by her mother and my father adopted her when she was very small), but her birth father died years ago. We know he was an "interesting" man. He was wild and a convict (not even an EX-con. He was on the run from legal authorities when he dated my sister's mother). My sister met him later in life and had a hint of a relationship with him, but I never met him. I have no idea if this woman could be related to her.

It's such an odd position to be in. The resemblance could be purely coincidental. Then again, since my sister was adopted, this woman could be a relative. It's so bizarre to look at someone you've just met and think, "You could be related to my sister."