Just need to vent....

So a little back story.

My fiancé and I met through a common friend and yes he is 6 years younger then me, I told him from the beginning that his parents were not going to like me and that he should find someone else basically. The reasons why his parents won’t like me is because I have 5 kids already and going through my 2nd divorce, he thought I was lying about his parents. Forward to now, it’s been almost 2 years since him and I started seeing each other and I honestly just want to punch his mom in her face. It’s time for her to accept me. Him and I have been through so much in the last year and a half that most couples won’t go through their whole relationship/marriage. We have lived together since November of 2017. Everyone else has accepted me by now and she hasn’t, what can I do to help her along with it. Keep in mind he is the only child and his parents have always bailed him out of everything he has ever gotten into.