Girls, If a girl can't look at you but her friends do?

So there is this girl that I have gotten to know very well through some lectures and classes, and today she acted very weird. When I was on my way to class on campus, I saw her talking to a friend by a tree while pointing at me. As soon as I turned to look she put her hand down and turned her back, but her friend kept staring at me the whole time until I got to my class. Girls, why would you ask your friends to stare at you, but not do it yourself? All help appreciated, thanks!
Girls, If a girl can't look at you but her friends do?
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