Feeling guilt

Fiancé has siblings, one of which he is adamant about not inviting to our wedding, which we’re about to send out invitations. She has been horrific to us almost our entire relationship. It’s basically a cluster of her constantly talking shit about us to people, being aggressively jealous of us having a child before her, her lying and twisting our image to whoever will listen, and whenever we see her at gatherings she will just brag about random things trying to rub in our face while we nod and smile and congratulate her anyway. Also about 3 years ago she attacked my fiancé which me and the younger sister witnessed, then called the cops and twisted the story - with her record, they knew her quite well and escorted her off the property. She also made a kill list about 3 years ago which the younger sister showed us which included me, fiancé, her dad, grandma and other names we didn’t recognize. Last time we went out to dinner with her with the younger sister for the younger sisters birthday, she talked about their dads future demise (who is not dying) and wanting the house to be in her name. She now acts as if none of these things ever happened and believes she will be attending the wedding, but due to limited guest count and fiancés adamant stance on keeping her far away, she will not be coming. I am a people pleaser, I hate drama and wanted to invite her just so she doesn’t lash out. WHY do I feel guilty about not inviting her? How do I let go of this nagging guilt like I’m the bad person and evil sister in law trying to tear apart the family? I feel it’s fiancés decision but it’s still bugging me, and he says he doesn’t want a scene and just plans on not sending her an invitation. Why do I feel so guilty?