I am a 9th grade student and my best friend's sister says hi/bye to me everyday. She is in 7th grade

I am a 9th grade student and my best friend is in 8th grade. (We know each other since 4th grade). His sister is in 7th grade & she one day shake hands with me to wish me ******** ***. After that day, everyday she says hi/bye to me. When I enter the school she is excited to see me and says hi then says best of luck for the exams. She also touches me in arms and laughs a lot & smiles while looking at me from a distance away. Why she does this? What does it mean?

Baby I will only quote Mark sine he says ' understanding a girl is like downloading a 5 gb file on s 2 kbps speed which at the completion will get you you error, invalid file or file corrupt. I know it sounds technical but bear it and take it easy