My Wife Secretly Invited My Estranged Sister to Our Daughter's Birthday Party - I Feel Completely Betrayed

I need some perspective here. My relationship with my sister completely fell apart 4.5 years ago, and it's been a nightmare ever since.

Background: The breaking point came during my parents' brief separation. During a call with my sister and wife, I calmly pointed out that my sister had let our mom live with her for 4 months away from dad, so she couldn't be surprised they were splitting. She wanted me to rage against our dad, but I refused to take sides. She took this as me blaming her for their divorce (which wasn't true) and completely cut us off - blocking us on all social media and having her husband do the same.

Despite my apology text and my wife personally going to their house to try to mend things, the relationship has remained toxic. We did have one hour-long phone call two years ago, but she never apologized or admitted any wrongdoing.

The Ongoing Issues: * She's verbally abusive to our parents * Everyone walks on eggshells around her or risks being blocked * She threatens to keep her kids from seeing our mom if mom doesn't comply with her demands * She's done other concerning things (like hosting events at her boutique while COVID-positive)

For the past 4 years, I've maintained a firm boundary: we don't go to their house, and they don't come to ours.

The Betrayal: Yesterday, I found out from my other sister that my wife secretly invited my estranged sister's family to our daughter's 5th birthday party at our house. My wife never told me this - I only found out because my other sister accidentally mentioned it.

The party has already happened, and I had to put on a brave face and pretend everything was fine while dying inside. My wife claims she did it "for the kids" because our daughter should see her cousins.

I feel completely betrayed. My wife knew how painful this relationship is for me, yet she went behind my back and invited them anyway. How could she justify this as "doing it for the kids/family" while knowingly causing me so much pain? Why do my sister's feelings seem to matter more than mine to my own wife?

I haven't confronted my wife yet because I'm still processing this betrayal. How should I approach this conversation?