She does not wave me

A long time ago I dated just once with a girl. Since then, when I come across with her we just speak few sentences. She told me she came back with her ex-boyfriend and she did not want people see her with other guys.
To be honest I do not relly her version.
But today I come across with her, very close, and she ignored me. She did not wave me.
If I see tomorrow I will ask her for this behaviour. I got angry because I do not like this lack of respect.
I can understand I do not like her, but I cannot understand this manners. Why?.

Sometimes people act in this way, and there is nothing we can do to change the way they act. If she ignores you, why waste time worrying about it? It would be sensible to forget about her, and get on with your life.