People who have stopped contact due to a falling-out have a tendancy to reinforce their belief in the reasons why they fell out in the first place. They become more sure of their position and become more sure of the intentions / motives of the person they fell out with.
Without speaking to her you don't know why she ran away like this, but perhaps she has built up "the problem" in her head so that it is much more serious than you consider it to be, and was worried about a confrontation with you. Maybe she was afraid of you, maybe she was afraid of what she might say. It doesn't automatically mean there was any legitimate reason for her to fear you in this way, but her perception might seem real to her, especially if she has mulled over "the problem" and increasingly sees it in a one-sided manner.
It could equally be that she feels guilty that she sided against you, and the sight of you today overwhelmed her with guilt. People who know they are wrong but don't know how to deal with it sometimes do "odd" things like this - it's easier to run away than have an adult discussion.
People do act strangely like this though. I saw an old friend who I hadn't spoken to in a while in the supermarket once - she caught my eye, put down her basket and literally ran out of the shop. I genuinely don't know why, we hadn't had any kind of falling out (that I was aware of) - we'd just fallen out of touch.
My only advice is to keep the door open to restoring communication with her. You can't force her to communicate with you, but you can be receptive to it whenever she eventually decides that she's an adult and it's time for her to get over this.