Trying to get the girl...is she interested or not?

I met this girl in 7th grade and had a crush on her,but back then she hated me(so she played it).Time passed,and I didn't see her until the end of highschool.So many years went by without even hearing from her. Then out of nowhere i saw her at church and approached her,same time her dad just popped out and she left.She gave me a huge smile. Then again,i saw her and this time she was sitting right beside me, but at that time i was speaking to my mom, i commented something funny and i heard her giggle right beside me. Then, the last time i saw her was when i was preparing some paperwork before leaving, i was walking along side a friend and she passed beside me with some friends and from the side of my eyes i caught a glimpse of her looking at me.Sadly,however, i left the country to pursue university education. So i tried chatting with her on facebook 3 different times,yet she never answer. Just from assumpitons,is it that she get's nervous when talking to me or is she simply not interested?