Its just sounds like simple jealousy to me. To just ignore her completely I recommend just blocking her so she wont be able to see you or you see her and she will not be able to back talk you in whisper.
If this offense does get out of control to where she is constantly harassing you, then take screenshots of the chat and send them to a MOD or Admin. Make you sure you get a picture of there username so they will know who to take care of. Mods/Admins do not take actions in punishing someone without physical evidence of the actions so make sure you get snapshots.
STAFF (http://feral-heart.com/index.php?option=com_content&view=article&id=28&Itemid=52)
~Good luck hun