Maybe she is not as indifferent as you think.. My ex best friend (who happened to be BPD) acted out indifference as a weapon of cruelty and ultimate control over the other person.
When someone is basically indifferent to your existence. Especially when you're emotionally invested in them.
I'd even prefer it if she was upset with me...
*sigh*
With women, it's always difficult to tell. Although she could be indifferent to you, there's always the option that she's either shy or slightly scared to speak with you. Also, I read somewhere that women may ignore a man purposefully to test, to flirt, to somehow provoke. Thus the saying 'Women are from Venus, Men are from Mars' is quite fitting to the situation. Maybe you should have a chat with her about it. I'm sure there's a reasonable explanation. I hope this was of any help!