Stepmom and mom of groom

I am mother of the groom, my son had a stepmom who helped raise him and she and his dad divorces but she is still a big part in his life. She hates me! She was listed as mother of the groom on the wedding party. I was too but it still hurt. She was invited to bridal shower and I was not nor was my family. We threw the couple a separate shower just so we could celebrate them. Now I find out that the rehearsal dinner is at ex stepmoms new husband's parents house. How do I navigate this, I have been given an invite from my soon to be daughter n law but this is going to really be difficult for me to go to a place where I know I'm not wanted or liked. This whole wedding has put me in a deep depression because I feel like stepmom has taken the reigns as mom and I'm just along for the ride. I do not want to ever hurt my son but every time I turn around this woman is in the position where I should be. I am his mother. What do I do. ?