What's up with my neighbor who ignores me?

my neighbor totally ignores me, won’t say hello, even when i have greeted her. i am curious what her problem with me is. i am debating whether to approach her and ask her why, but don’t want to scare her, and if i ask her and she’s nasty about it i will definitely tell her off. the other option is to forget the issue, but i am really curious what i have done. she does not appear to be this way toward anybody else, so it seems to be an issue she has with me. i have barely had any discussions with her and so i don’t think i have offended her in the past, that i know of. should i ask her why she ignores me or should i just ignore her back?