Should I message her?

Knowing people's intentions is something that I suffer with the most, when I get to know someone it becomes easier but it's whether or not they want to know me is the obstacle. I am trying to live my life as normally as possible but it can be very hard, on farthers day my family went for breakfast instead of a dinner for various reasons. I saw somebody there that I went to school with and we made eye contact a few times. It's her birthday today (Facebook has popped up with well wishers as we have over 100 mutual friends even though we are not 'friends' on Facebook!' I was wondering if I should message her? it's terrifying not knowing what emotions people are feeling and I'm scared of being humiliated. One part of me thinks it would be exciting and the other is nervous of the out come. any advice would be awesome thank you.