Ignoring the other aspects of your sad story and addressing only the question at hand:
You are to "kill her with kindness". As Catholics, as hard as it can be, we are obliged to be cordial to people, especially those who irritate us most. You at least are doing the right thing to be trying to improve relations and be nice to her. This is a practise of patiance, which can be a hard virtue to acquire. You should pray for her, and all the more so since yall don't get along. Pray to the Holy Ghost for guidance and Wisdom, trust in Him and things will improve; maybe not in the way you would expect, but things shall, non the less.
The Virtue of Charity demands this as well
It is in the 8 Beatitudes: "Love those who hate you. Bless those who curse you. Blessed are the peacemakers, etc".
Others here will probably give better answers, but I hope this helps! :)
You'll be in my prayers!