Girl's Behavior

What does it mean when a girl covers her face like this?

I like this girl a lot but I don't know how she feels. We were in a group and we were talking about how one day we should exchange and do each others' homework randomly. One of my friends told the girl "you should do him (pointing at me) and she turned red and started giggling nonstop and covering her face with a piece of paper, then lowered a bit and looked at me and we all started laughing, then he added "do his homework". Does that reaction mean anything at all? She usually acts "tough" and sarcastic around me but nice to others, so its hard to decipher what she is thinking.
What does it mean when a girl covers her face like this?
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