Please read. need help! Friend problem1.why is she doing this?

about 7 months ago, i met this girl at my new job and we became instant friends we had this real connection. we would hang out everyday and my family even invited her family to my brothers wedding in Florida expenses paid. She even trusted me with some of her biggest secrets. But about 2months ago we got into a argument because she got mad that i didn't tell her about some family issues that were going on. Personally i thought it was none of her Business I dont like to involve my friends in family drama. She later found out about it and she started yelling at me saying she couldn't trust me. She then completely shut me out of her life. I apologized a million times and she told me she understood but she didnt want to be friends anymore. I was so hurt i tried everything. she did once tell me that she doesnt have a lot of friends and that she perfers to be alone. But i dont get how she is one of the nicest, kindest, outgoing people i know, she seems to be that person who makes friends very easily everybody likes her but yet she has no friends? I first i thought it was just me but ive noticed that she tends to make friends and drop them in a second. Ive know some off the people shes once hung out with and they were great people yet she's no longer friends with them.. ive noticed a pattern in this, its not like shes some mean antisocial person shes just the opposite? How do you explain that? Whats up with that?