It’s very upsetting. But hopefully you two could move on from this bad incident. Things happen.

Personally I’d apologize and hope she would apologize too and maybe I’d suggest to meet just two of you. Your mom means well and is overprotective, the way moms could certainly be, but you aren’t a little girl. Two 50+ ladies could hopefully make peace with each other without moms mediating. Personally I’d prefer it that way

My stepdaughters have difficult relationship with each other and currently aren’t speaking to each other. It’s a very complicated situation and source of pain for my husband. But we’ve learned that we can’t fight that battle for them and we can’t demand reconciliation. They need to figure it out or not figure it out. But we can’t fix their relationship because it could actually make it worse.

It’s a tough situation all around. I understand. I’d be very heart broken to have a rift with my brother. I hope it will be resolved soon for both of you