This can mean aLot of things. There is no pat answer to your question. Was she Laughing when she crossed her arms? Was she rude? Was she just getting comfortabLe?
In my view, if a girL taLks to me for more than five minutes, there is onLy one of two things going on. Either she is sexuaLLy attracted to me, or she feeLs friendLy toward me. If she onLy feeLs friendLy toward me then this must mean that she is amused by what I am saying. If she is amused then there is stiLL a chance that I can attract her to myseLf. Think about it, if an attractive woman is taLking to you for more than five minutes then there is aLways a chance that you can attract her.
Why?
Because if she's a hot girL then she has many opportunities to taLk to many guys every day. Why wouLd she waist five minutes on me? She must find some kind of attractive quaLity in me that she doesn't find in other men, otherwise she wouLd have Left Long ago.