I seen a strange sighting. Virgin Mary?

This might be a little strange but about a year ago I visited my friend. It was very gray and dark outside. She and I were talking about religion out on the front steps of my school. No one was around but me and her. Every time she mentioned "Yahweh" it started to get silent. So we were chatting away,.. arguing and debating. I looked at her as she scowled and stared off into the distance. All of a sudden she was like "Wtf Diana!! Do you see that thing over there?" I looked over in the direction and my eyes got wide. In the football field there was this lady that was soo bright white(everything on her, including skin color). She had a long veil that reached the ground. I thought it was someone playing a joke but then I realized that this woman wasn't walking on the ground. More like walking on air about a foot above. She kept on coming closer. My friend started freaking out. She got enough guts to approach this thing. She was like "**** it I'm not scared." Then this figure started to back away every time she came closer then disappeared. I told her to stop and I started crying because I have no idea what it was. I called my step dad to come pick me up immediately. I told him what happened and he was like "Maybe it's time to change your views." I'm an atheist, so I'm not a crazy religious person to make this kind of stuff up. I went back to her house the next day because we were so shocked of what happened. Again, it was a dark afternoon and we approached the school, no one was there. Then my friend said "Omg, she's right there walking on the side." I looked and I couldn't handle it so I demanded to go back home. The third time we went, we saw nothing. I'm wondering what you all think of this? Is this some sort of sign? It looked exactly like the Virgin Mary....This happened in Chicago, IL and at that time I was 17 years old. I ure you I wasn't drunk or on anything when this took place. Thank you.