If you were looking at her and then she looked at you at the same time and noticed you looking at her- maybe she just wanted to be friendly since you were already looking at each other, so she smiled at you.
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Your Aspie score: 120 of 200 ; Your neurotypical (non-autistic) score: 90 of 200
You seem to have both Aspie and neurotypical traits
Self-DX: Extreme Introvert, possibly with ADHD-Primarily Inattentive; Official DX: Generalized Anxiety Disorder