She used to love me and I loved her very much, we were inseparable. But I made a mistake and hurt her, but badly, and she has hated me ever since. We exchanged a few words once or twice over the years, but she still hates me.
I want to make it right.
Perhaps write her a long letter/email explaining how you know you messed up, but will never do it again, and are willing to do what it takes to make it right with her.
Often, someone will continue hating the person, because they ruined what could have been a happy and permanent relationship.
You can also do a Venus square or a working with Wunjo and/or Gebo rune to help.