@livelaughlove21 Because family harmony is worth something. Not inviting her can be the start of her not being invited to her cousin’s wedding, etc., etc. If the aunt isn’t going to make a scene it isn’t really a big deal, especially of the wedding is going to be rather large. Weddings are not always only about the bride and groom, it is also sometimes a family event. A reason for the family to be together. You paid for your wedding if I am not mistaken, but in many families the parents pay. That is why invitiations usually read Mr. and Mrs. Doe request the honour of your presence to the marriage of their daughter Jane to John Smith. I think most people agree the bride gets the most influence over the events, but family is usually considered in one way or another.
It isn’t all about money though. Even if the bride and groom are paying for everything it is worth inviting the aunt for family harmony assuming the family generally gets along. If the family is very broken and dysfunctional, then possibly not. We don’t know the exact situation.
The OP can be the one who unites rather than breaks apart the family. She needs to decide what would be most true to herself. Her aunt can decide not to go if she disapproves.
We don’t know the details of the OP’s situation, so it is difficult to know if our advice really fits her situation.
I wish I had invited some cousins who I didn’t to my wedding. I really regret it. I was not angry with them, people just had convinced me not to have “children” there, long story, and I was not very close to them anyway. They weren’t that young at the time. Tween and early teen. Somehow I knew enough to encourage my husband to have his brother at our wedding, even though his brother had just done a horrific thing to him and his mother. Really really bad. But, eventually the family has forgiven him, and it would have been quite sad if he had missed our wedding day. Many family matters are temporary. The wedding day is hopefully once in a lifetime.