Why Does my aunt hate me so much?

cause shes being a jerk, not much you can do about it

You can't change someone else's behavior. What you can do, however, is tell your aunt that you're aware of the situation that causes her to behave the way she does. Tell her that in your opinion, it's childish, and she needs to get over it. She will probably get really angry about having someone call her attention to her behavior, but so be it. Someone needs to call her out, and you're the best person to do it.

That is tough. I suggest you make the first step. Maybe send her flowers on her birthday and her daughter's birthday. Say good things about them in front of your grandma. If you truly want to make the relationship better between you and them, then you just have to be the bigger person. If you keep being nice to them and they do not change their behavior, at least you know that you are not the problem. An other way is to find a chance to talk to her privately. Find out why she is still mad at you all these years. Confirm with her it was because of the birth issue. Tell her it was not your decision. Tell her you love her and want the relationship between you and her to be better. That can back fire depends on what kind of person she is. She could get totally defensive and insulting. At that point you just walk away and don't make it worse than it was. But in normal circumstances, things should improve after the talk (at least temporary). But, I can only say, good luck to you.

Maybe your Aunt had a bad experience with your Father. She's implicating you about problems caused by your Father.

Ask her (nicely) if she would be happy if you skipped over her birthday and always bragged about someone else that was maybe born close to her(family or friend)

be close to her do anything yo can do just to have a positive impression to her